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<!--XBRL Document Created with Wdesk from Workiva-->
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    <link:label id="lab_us-gaap_SupplementalCashFlowInformationAbstract_08991a94-26f5-4061-967c-29ef9656d434_terseLabel_en-US" xlink:label="lab_us-gaap_SupplementalCashFlowInformationAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Supplemental Information:</link:label>
    <link:label id="lab_us-gaap_SupplementalCashFlowInformationAbstract_label_en-US" xlink:label="lab_us-gaap_SupplementalCashFlowInformationAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Supplemental Cash Flow Information [Abstract]</link:label>
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    <link:label id="lab_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_965e13af-cfd1-4118-8b45-bdfe5ff0c87c_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unrealized gains and losses on available-for-sale securities</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:to="lab_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_CommonEquityTierOneCapital_label_en-US" xlink:label="lab_us-gaap_CommonEquityTierOneCapital" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Common Equity Tier One Risk-Based Capital, Actual</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonEquityTierOneCapital" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonEquityTierOneCapital"/>
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    <link:label id="lab_us-gaap_LetterOfCreditMember_85ddbd46-5662-4ed0-ae20-695cb7d428c3_terseLabel_en-US" xlink:label="lab_us-gaap_LetterOfCreditMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial and similar letters of credit</link:label>
    <link:label id="lab_us-gaap_LetterOfCreditMember_label_en-US" xlink:label="lab_us-gaap_LetterOfCreditMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Letter of Credit [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LetterOfCreditMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LetterOfCreditMember" xlink:to="lab_us-gaap_LetterOfCreditMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit_2127c89a-31f5-4d78-b11b-85578ab541a7_terseLabel_en-US" xlink:label="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">State</link:label>
    <link:label id="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit_label_en-US" xlink:label="lab_us-gaap_CurrentStateAndLocalTaxExpenseBenefit" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current State and Local Tax Expense (Benefit)</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_ee2ad368-e768-4a35-ad27-8e570d6f7907_negatedLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Vested (in shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period</link:label>
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    <link:label id="lab_srt_ConsolidatedEntitiesAxis_7139e1af-e976-47a8-a636-36e8c2685a8a_terseLabel_en-US" xlink:label="lab_srt_ConsolidatedEntitiesAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Consolidated Entities [Axis]</link:label>
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    <link:label id="lab_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_18c21a70-6cf0-4110-b327-c1d9be9ecad3_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reasons for the difference between income tax expense and statutory federal income tax</link:label>
    <link:label id="lab_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_label_en-US" xlink:label="lab_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Amount [Abstract]</link:label>
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    <link:label id="lab_source_ProfessionalAndDirectorsFees_5449e537-ab07-4671-bc77-f3d6e0a65b3f_terseLabel_en-US" xlink:label="lab_source_ProfessionalAndDirectorsFees" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Professional fees</link:label>
    <link:label id="lab_source_ProfessionalAndDirectorsFees_label_en-US" xlink:label="lab_source_ProfessionalAndDirectorsFees" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Professional and Directors Fees</link:label>
    <link:label id="lab_source_ProfessionalAndDirectorsFees_documentation_en-US" xlink:label="lab_source_ProfessionalAndDirectorsFees" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element includes fees charged for services from professionals such as doctors, lawyers and accountants. Also includes expenses related to directors' fees which are fees paid by an entity to its directors. Directors fees may be paid in addition to salary and other benefits.</link:label>
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    <link:label id="lab_source_NumberOfDomesticAircraftLoanPools_9fe20e57-b7c1-44b5-a3ca-61bbc4bb40a1_terseLabel_en-US" xlink:label="lab_source_NumberOfDomesticAircraftLoanPools" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of domestic aircraft loan pools</link:label>
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    <link:label id="lab_source_NumberOfDomesticAircraftLoanPools_documentation_en-US" xlink:label="lab_source_NumberOfDomesticAircraftLoanPools" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of domestic aircraft loan pools</link:label>
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    <link:label id="lab_us-gaap_OtherIntangibleAssetsMember_70370b60-028a-4db5-bac9-327b23a0d7a1_terseLabel_en-US" xlink:label="lab_us-gaap_OtherIntangibleAssetsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other intangibles</link:label>
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    <link:label id="lab_source_TradePublicationsValuationTechniqueMember_0be32ad3-d08f-4f8a-94c4-21e15def6303_terseLabel_en-US" xlink:label="lab_source_TradePublicationsValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trade publications</link:label>
    <link:label id="lab_source_TradePublicationsValuationTechniqueMember_label_en-US" xlink:label="lab_source_TradePublicationsValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trade Publications Valuation Technique [Member]</link:label>
    <link:label id="lab_source_TradePublicationsValuationTechniqueMember_documentation_en-US" xlink:label="lab_source_TradePublicationsValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the trade publications valuation technique used to measure fair value.</link:label>
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    <link:label id="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_9fb74c6a-a2d9-473f-af2e-5c8ded3c7596_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Changes in the fair value of Level 3 assets measured on a recurring basis</link:label>
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    <link:label id="lab_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases_d2b7796f-9b29-4087-96ea-2fb1285877cd_terseLabel_en-US" xlink:label="lab_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income from reimbursements for personal property tax payments on operating leased equipment</link:label>
    <link:label id="lab_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases_label_en-US" xlink:label="lab_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Related to Reimbursements from Lessees on Operating Leases</link:label>
    <link:label id="lab_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases_documentation_en-US" xlink:label="lab_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income related to reimbursements from lessees for personal property tax on operating leases.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases" xlink:href="source-20211231.xsd#source_IncomeRelatedtoReimbursementsfromLesseesonOperatingLeases"/>
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    <link:label id="lab_us-gaap_DividendsCommonStockCash_fee4e4c4-c21d-4e3d-9de9-9844e1dca3da_negatedLabel_en-US" xlink:label="lab_us-gaap_DividendsCommonStockCash" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock dividend ($1.21, $1.13, and $1.10 per share for 2021, 2020 and 2019, respectively)</link:label>
    <link:label id="lab_us-gaap_DividendsCommonStockCash_label_en-US" xlink:label="lab_us-gaap_DividendsCommonStockCash" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Dividends, Common Stock, Cash</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DividendsCommonStockCash" xlink:to="lab_us-gaap_DividendsCommonStockCash" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_SecurityExchangeName_1c224824-93c6-4230-aabe-c46f8eaeef1a_terseLabel_en-US" xlink:label="lab_dei_SecurityExchangeName" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Security Exchange Name</link:label>
    <link:label id="lab_dei_SecurityExchangeName_label_en-US" xlink:label="lab_dei_SecurityExchangeName" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Security Exchange Name</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_SecurityExchangeName"/>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_1c7c543c-7d6e-4baa-9a1a-4c5edea97ec4_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Forfeited (in dollars per share)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months_3a65a79e-b6ba-45d0-9d9a-e72cfa53f3bb_terseLabel_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">7-12 months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months_label_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual Maturities, Time Deposits, $250,000 or More, Six Months Through 12 Months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months_documentation_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The amount of contractual maturities of domestic and foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more, for the period from six months through twelve months after the balance sheet date.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months" xlink:href="source-20211231.xsd#source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months" xlink:to="lab_source_ContractualMaturitiesTimeDeposits250000orMoreSixMonthsThrough12Months" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_3b9e6f51-9d83-44db-b4a7-e215241f29d0_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Weighted average remaining lease term</link:label>
    <link:label id="lab_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_label_en-US" xlink:label="lab_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Weighted Average Remaining Lease Term</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:to="lab_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract_1d0a1c9c-edf8-4c08-ae4b-c2ec90bf8339_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Amounts Not Offset in the Statement of Financial Condition</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract_label_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Liability, Fair Value, Amount Offset Against Collateral [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract" xlink:to="lab_us-gaap_DerivativeLiabilityFairValueAmountOffsetAgainstCollateralAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_2756ca90-18bc-4968-bc36-08cbe984bf47_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="lab_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativesPolicyTextBlock_bb7d733f-f237-4675-9105-8512ed6c052d_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativesPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Financial Instruments</link:label>
    <link:label id="lab_us-gaap_DerivativesPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_DerivativesPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivatives, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativesPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativesPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativesPolicyTextBlock" xlink:to="lab_us-gaap_DerivativesPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromMinorityShareholders_a9eab838-5386-4b98-8b10-107ddec735ff_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromMinorityShareholders" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in noncontrolling interests</link:label>
    <link:label id="lab_us-gaap_ProceedsFromMinorityShareholders_label_en-US" xlink:label="lab_us-gaap_ProceedsFromMinorityShareholders" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from Noncontrolling Interests</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMinorityShareholders" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromMinorityShareholders"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromMinorityShareholders" xlink:to="lab_us-gaap_ProceedsFromMinorityShareholders" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months_eadaaf58-d0f3-42b7-800d-a97d84256689_terseLabel_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Over 12 months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months_label_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual Maturities, Time Deposits, $250,000 or More, after 12 Months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months_documentation_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The amount of contractual maturities of domestic and foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more, after twelve months from the balance sheet date.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months" xlink:href="source-20211231.xsd#source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months" xlink:to="lab_source_ContractualMaturitiesTimeDeposits250000orMoreafter12Months" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_27e45da5-1a8a-48f3-b430-e67d2a615d97_periodStartLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance at the beginning of the period (in shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_f5007666-7b9a-4133-b41e-3f72f5e3b471_periodEndLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance at the end of the period (in shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:type="arc" order="1"/>
    <link:label id="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs_8702df95-4bf2-4104-8ac3-c22339e4d9c1_totalLabel_en-US" xlink:label="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net charge-offs (recoveries)</link:label>
    <link:label id="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs_label_en-US" xlink:label="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable Allowance for Credit Losses Net Write Offs</link:label>
    <link:label id="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs_documentation_en-US" xlink:label="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of direct write-downs of financing receivables charged against the allowance net of recoveries.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs" xlink:href="source-20211231.xsd#source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs" xlink:to="lab_source_FinancingReceivableAllowanceForCreditLossesNetWriteOffs" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InventoriesMember_534b5599-b6ab-4544-bf82-3e5552f4880c_terseLabel_en-US" xlink:label="lab_us-gaap_InventoriesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventory</link:label>
    <link:label id="lab_us-gaap_InventoriesMember_label_en-US" xlink:label="lab_us-gaap_InventoriesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Inventories [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoriesMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoriesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InventoriesMember" xlink:to="lab_us-gaap_InventoriesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingLeaseLeaseIncome_b3af6a96-939d-41f8-87ac-6085a27d2bb9_verboseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseLeaseIncome" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Rental income from (reimbursements to) subsidiaries</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
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    <link:label id="lab_us-gaap_InterestRateDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue_d9b06afd-67a6-4113-a3e8-b5f7868d18ef_terseLabel_en-US" xlink:label="lab_us-gaap_InterestRateDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest rate swaps</link:label>
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    <link:label id="lab_source_ScheduleLongTermDebtAndMandatorilyRedeemableSecuritiesTableTextBlock_aff9c464-b6f0-48aa-8e00-e999981bf0d1_terseLabel_en-US" xlink:label="lab_source_ScheduleLongTermDebtAndMandatorilyRedeemableSecuritiesTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of long-term debt and mandatorily redeemable securities</link:label>
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    <link:label id="lab_us-gaap_TimeDepositMaturitiesAfterYearFive_50db56f8-e0a5-4991-86db-ef68db2ed694_terseLabel_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesAfterYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Thereafter</link:label>
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    <link:label id="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_ab07f089-b208-49e8-a07b-2b9ff780e14f_terseLabel_en-US" xlink:label="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of reclassifications out of accumulated other comprehensive income</link:label>
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    <link:label id="lab_source_ShortTermDebtTerm_9eb32cce-e5b2-442e-9438-104c5165882d_terseLabel_en-US" xlink:label="lab_source_ShortTermDebtTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Term of short-term debt</link:label>
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    <link:label id="lab_source_ShortTermDebtTerm_documentation_en-US" xlink:label="lab_source_ShortTermDebtTerm" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the term of short-term borrowings.</link:label>
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    <link:label id="lab_us-gaap_AmortizationOfIntangibleAssets_4be46747-610f-47ec-966f-807d6cb1c482_terseLabel_en-US" xlink:label="lab_us-gaap_AmortizationOfIntangibleAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Intangible asset amortization</link:label>
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    <link:label id="lab_us-gaap_DerivativeCollateralObligationToReturnCash_3a63d655-1517-46aa-9c6b-ec8650e322ad_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeCollateralObligationToReturnCash" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash collateral received</link:label>
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    <link:label id="lab_us-gaap_DeferredTaxAssetsLiabilitiesNet_26106765-0a51-440e-a3e4-abc705994266_totalLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsLiabilitiesNet" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Net, Total</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNet"/>
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    <link:label id="lab_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_ba8d331d-8252-4214-83a8-150da216098f_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Weighted average discount rate</link:label>
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    <link:label id="lab_us-gaap_SubsidiarySaleOfStockAxis_a9a3dc27-f088-40ea-95c1-5de85a947240_terseLabel_en-US" xlink:label="lab_us-gaap_SubsidiarySaleOfStockAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subsidiary, Sale of Stock [Axis]</link:label>
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    <link:label id="lab_us-gaap_SubsidiaryOfCommonParentMember_25482079-c132-443f-a6b3-03b7d75d554a_terseLabel_en-US" xlink:label="lab_us-gaap_SubsidiaryOfCommonParentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Bank subsidiaries</link:label>
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    <link:label id="lab_us-gaap_PreferredStockValue_73218c1e-dafc-4421-8b1a-a7026cac0ee1_terseLabel_en-US" xlink:label="lab_us-gaap_PreferredStockValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred stock; no par value Authorized 10,000,000 shares; none issued or outstanding</link:label>
    <link:label id="lab_us-gaap_PreferredStockValue_label_en-US" xlink:label="lab_us-gaap_PreferredStockValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred Stock, Value, Issued</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" xlink:to="lab_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_68014a76-6e3c-40f9-badf-41ef6536dd13_terseLabel_en-US" xlink:label="lab_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable interest entity, not primary beneficiary</link:label>
    <link:label id="lab_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_label_en-US" xlink:label="lab_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Interest Entity, Not Primary Beneficiary [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
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    <link:label id="lab_us-gaap_RetainedEarningsMember_c5caf9ab-3d31-4082-9d61-7c1e3f3ddcb3_terseLabel_en-US" xlink:label="lab_us-gaap_RetainedEarningsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retained Earnings</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
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    <link:label id="lab_us-gaap_Deposits_9c16cac4-90e2-4687-a278-69212f4e6289_totalLabel_en-US" xlink:label="lab_us-gaap_Deposits" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total deposits</link:label>
    <link:label id="lab_us-gaap_Deposits_label_en-US" xlink:label="lab_us-gaap_Deposits" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deposits</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Deposits" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Deposits"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Deposits" xlink:to="lab_us-gaap_Deposits" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestExpenseAbstract_975dc552-e7a5-4604-b49b-58f4cd209621_terseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest expense:</link:label>
    <link:label id="lab_us-gaap_InterestExpenseAbstract_ffc7ef1e-dc12-478f-a90f-d70ed2d6d818_verboseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseAbstract" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expenses:</link:label>
    <link:label id="lab_us-gaap_InterestExpenseAbstract_label_en-US" xlink:label="lab_us-gaap_InterestExpenseAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Expense [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestExpenseAbstract" xlink:to="lab_us-gaap_InterestExpenseAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ImpairmentChargesOnLeasedEquipment_afa5b8d4-2e33-413b-8937-f653e37e56b4_terseLabel_en-US" xlink:label="lab_source_ImpairmentChargesOnLeasedEquipment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairment charges on leased equipment</link:label>
    <link:label id="lab_source_ImpairmentChargesOnLeasedEquipment_label_en-US" xlink:label="lab_source_ImpairmentChargesOnLeasedEquipment" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ImpairmentChargesOnLeasedEquipment</link:label>
    <link:label id="lab_source_ImpairmentChargesOnLeasedEquipment_documentation_en-US" xlink:label="lab_source_ImpairmentChargesOnLeasedEquipment" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairment charges on leased equipment</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ImpairmentChargesOnLeasedEquipment" xlink:href="source-20211231.xsd#source_ImpairmentChargesOnLeasedEquipment"/>
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    <link:label id="lab_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_03e8ec83-b5e9-4565-b930-60937226de24_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amortized cost of loans and leases, segregated by class, with delinquency aging and nonaccrual status</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Past Due [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
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    <link:label id="lab_us-gaap_InvestmentIncomeNonoperatingAbstract_993ade75-96b7-4c4e-85a4-d0c8aa2e7473_terseLabel_en-US" xlink:label="lab_us-gaap_InvestmentIncomeNonoperatingAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income:</link:label>
    <link:label id="lab_us-gaap_InvestmentIncomeNonoperatingAbstract_label_en-US" xlink:label="lab_us-gaap_InvestmentIncomeNonoperatingAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment Income, Nonoperating [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNonoperatingAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentIncomeNonoperatingAbstract"/>
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    <link:label id="lab_source_AppraisalsTradePublicationsAndAuctionValuesValuationTechniqueMember_d94c94c2-a72a-4e47-88ef-3de76e801334_terseLabel_en-US" xlink:label="lab_source_AppraisalsTradePublicationsAndAuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Appraisals trade publications and auction values</link:label>
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    <link:label id="lab_source_AppraisalsTradePublicationsAndAuctionValuesValuationTechniqueMember_documentation_en-US" xlink:label="lab_source_AppraisalsTradePublicationsAndAuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the appraisals trade publications and auction values valuation technique used to measure fair value.</link:label>
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    <link:label id="lab_source_InterestExpenseLongTermDebtAndMandatorilyRedeemableSecurities_96ab72ed-3fd4-4375-a90e-775b1602c601_terseLabel_en-US" xlink:label="lab_source_InterestExpenseLongTermDebtAndMandatorilyRedeemableSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-term debt and mandatorily redeemable securities</link:label>
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    <link:label id="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract_4d2a0395-0b1c-4c50-80ca-8ca5a907eb8a_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Instruments and Hedging Activities Disclosure [Abstract]</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentLineItems_aaa01ef4-5922-42d4-9c7e-b35f71a0b32a_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Premises and equipment</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentLineItems_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
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    <link:label id="lab_dei_EntityWellKnownSeasonedIssuer_f40a7c18-3d05-40b2-b786-3cb087505dfc_terseLabel_en-US" xlink:label="lab_dei_EntityWellKnownSeasonedIssuer" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Well-known Seasoned Issuer</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityWellKnownSeasonedIssuer" xlink:to="lab_dei_EntityWellKnownSeasonedIssuer" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_9fd99997-f70b-406c-a627-4ec99920488d_totalLabel_en-US" xlink:label="lab_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Comprehensive income</link:label>
    <link:label id="lab_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_label_en-US" xlink:label="lab_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
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    <link:label id="lab_us-gaap_OtherShortTermBorrowings_6cdd110c-b3f3-4dc6-9219-90fd05589dd4_terseLabel_en-US" xlink:label="lab_us-gaap_OtherShortTermBorrowings" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other short-term borrowings</link:label>
    <link:label id="lab_us-gaap_OtherShortTermBorrowings_label_en-US" xlink:label="lab_us-gaap_OtherShortTermBorrowings" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Short-term Borrowings</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherShortTermBorrowings" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherShortTermBorrowings"/>
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    <link:label id="lab_us-gaap_ProvisionForLoanAndLeaseLosses_8230cafc-93c0-4535-adba-95f66613e6e7_terseLabel_en-US" xlink:label="lab_us-gaap_ProvisionForLoanAndLeaseLosses" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">(Recovery of) provision for credit losses</link:label>
    <link:label id="lab_us-gaap_ProvisionForLoanAndLeaseLosses_label_en-US" xlink:label="lab_us-gaap_ProvisionForLoanAndLeaseLosses" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Provision for Loan and Lease Losses</link:label>
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    <link:label id="lab_us-gaap_SecuritiesSubjectToMandatoryRedemptionMember_2126337b-638a-4227-bd48-65f200e77e21_terseLabel_en-US" xlink:label="lab_us-gaap_SecuritiesSubjectToMandatoryRedemptionMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Securities subject to mandatory redemption</link:label>
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    <link:label id="lab_us-gaap_EarningsPerShareBasic_2093fc41-6ea1-4f60-baa6-addde97452ef_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareBasic" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Basic net income per common share, in dollars per share</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareBasic_a64a11a0-ff51-481f-9bec-b8fa1d163e27_verboseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareBasic" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Basic earnings per common share (in dollars per share)</link:label>
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    <link:label id="lab_us-gaap_ConsumerLoanMember_8527ec85-a5ac-4e2a-9d4d-364005bedf5c_terseLabel_en-US" xlink:label="lab_us-gaap_ConsumerLoanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Consumer</link:label>
    <link:label id="lab_us-gaap_ConsumerLoanMember_label_en-US" xlink:label="lab_us-gaap_ConsumerLoanMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Consumer Loan [Member]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ConsumerLoanMember" xlink:to="lab_us-gaap_ConsumerLoanMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivablesTextBlock_a9d112c1-219b-4646-b2f9-d3a4f631fc8f_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivablesTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan and Lease Financings</link:label>
    <link:label id="lab_us-gaap_FinancingReceivablesTextBlock_label_en-US" xlink:label="lab_us-gaap_FinancingReceivablesTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivables [Text Block]</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis_430f72ca-ce5e-40b0-b279-d85bb665e4c1_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Due after five years through ten years</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_72119fab-d85e-44a5-a2ae-13367640db51_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in investing activities</link:label>
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    <link:label id="lab_us-gaap_FinancingReceivables30To59DaysPastDueMember_4616a72c-d060-4001-bb11-61ef93a1ec67_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">30 to 59 Days Past Due</link:label>
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    <link:label id="lab_srt_ScheduleOfCondensedBalanceSheetTableTextBlock_c4673b55-5e0c-49bf-9454-1774a68b5449_terseLabel_en-US" xlink:label="lab_srt_ScheduleOfCondensedBalanceSheetTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of statements of financial condition</link:label>
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    <link:label id="lab_source_LessorOperatingLeaseAccumulatedDepreciation_0f3a2c74-0b4e-4b44-ac37-b5d0552f30b2_negatedLabel_en-US" xlink:label="lab_source_LessorOperatingLeaseAccumulatedDepreciation" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated depreciation</link:label>
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    <link:label id="lab_source_TrustandWealthAdvisoryFeesPolicyTextBlock_5aea3467-4925-45ac-8428-d202950412a0_terseLabel_en-US" xlink:label="lab_source_TrustandWealthAdvisoryFeesPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trust and Wealth Advisory Fees</link:label>
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    <link:label id="lab_source_FinancingReceivableModificationsSubsequentPaymentDefaultPeriodPastDue_75fcbe60-029c-4cfd-83aa-b9be5e6fe78e_terseLabel_en-US" xlink:label="lab_source_FinancingReceivableModificationsSubsequentPaymentDefaultPeriodPastDue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Default threshold</link:label>
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    <link:label id="lab_us-gaap_InvestmentIncomeDividend_dbb9fc6d-d5ba-4ce2-a8f8-cbaf3247d261_terseLabel_en-US" xlink:label="lab_us-gaap_InvestmentIncomeDividend" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Dividends from bank subsidiary</link:label>
    <link:label id="lab_us-gaap_InvestmentIncomeDividend_label_en-US" xlink:label="lab_us-gaap_InvestmentIncomeDividend" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment Income, Dividend</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest" xlink:to="lab_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer_0a1ab048-b856-478a-b0f5-53c8283785ca_terseLabel_en-US" xlink:label="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy with Capital Buffer Amount</link:label>
    <link:label id="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer_label_en-US" xlink:label="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Capital Required For Capital Adequacy With Capital Buffer</link:label>
    <link:label id="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer_documentation_en-US" xlink:label="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The minimum amount of Total Capital required for capital adequacy purposes with capital buffer under the regulatory framework for prompt corrective action.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:href="source-20211231.xsd#source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:to="lab_source_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_SubsidiariesMember_8078c5d3-0cc2-48ed-9227-17393dcb660f_terseLabel_en-US" xlink:label="lab_srt_SubsidiariesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">1st Source Bank</link:label>
    <link:label id="lab_srt_SubsidiariesMember_label_en-US" xlink:label="lab_srt_SubsidiariesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subsidiaries [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SubsidiariesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_SubsidiariesMember" xlink:to="lab_srt_SubsidiariesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxAssetsGross_5d9d1624-a623-4bf3-9c92-bce56326e32a_totalLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsGross" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total deferred tax assets</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsGross_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsGross" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Gross</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsGross" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsGross"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxAssetsGross" xlink:to="lab_us-gaap_DeferredTaxAssetsGross" xlink:type="arc" order="1"/>
    <link:label id="lab_source_FederalTaxCreditsRecognizedInTaxExpense_68d28be1-3144-46c2-bfe7-316b3a700ab6_terseLabel_en-US" xlink:label="lab_source_FederalTaxCreditsRecognizedInTaxExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal tax credits recognized in tax expense</link:label>
    <link:label id="lab_source_FederalTaxCreditsRecognizedInTaxExpense_label_en-US" xlink:label="lab_source_FederalTaxCreditsRecognizedInTaxExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal Tax Credits Recognized In Tax Expense</link:label>
    <link:label id="lab_source_FederalTaxCreditsRecognizedInTaxExpense_documentation_en-US" xlink:label="lab_source_FederalTaxCreditsRecognizedInTaxExpense" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal income tax credits related to affordable housing and community development tax-advantaged investments in tax expense</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_FederalTaxCreditsRecognizedInTaxExpense" xlink:href="source-20211231.xsd#source_FederalTaxCreditsRecognizedInTaxExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_FederalTaxCreditsRecognizedInTaxExpense" xlink:to="lab_source_FederalTaxCreditsRecognizedInTaxExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter_eb1fe498-a2ea-4ad9-9639-a6c333f614dd_terseLabel_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Thereafter</link:label>
    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter_label_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, after Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter" xlink:to="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedThereafter" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityCommonStockSharesOutstanding_e5aa9049-f580-4853-91f3-540c041858ce_terseLabel_en-US" xlink:label="lab_dei_EntityCommonStockSharesOutstanding" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Common Stock, Shares Outstanding</link:label>
    <link:label id="lab_dei_EntityCommonStockSharesOutstanding_label_en-US" xlink:label="lab_dei_EntityCommonStockSharesOutstanding" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Common Stock, Shares Outstanding</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityCommonStockSharesOutstanding" xlink:to="lab_dei_EntityCommonStockSharesOutstanding" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions_719544a2-b334-46b5-a1c6-d4225daa53a6_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">New loans and other additions to related parties</link:label>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions_label_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases Receivable, Related Parties, Additions</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions" xlink:to="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_8e5d62a8-42e6-4408-bfeb-8c9008b16d0d_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Unrealized Gains</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:to="lab_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityAddressStateOrProvince_c9bebe8c-768b-4e28-9c5f-510f87b38f88_terseLabel_en-US" xlink:label="lab_dei_EntityAddressStateOrProvince" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, State or Province</link:label>
    <link:label id="lab_dei_EntityAddressStateOrProvince_label_en-US" xlink:label="lab_dei_EntityAddressStateOrProvince" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, State or Province</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressStateOrProvince"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityAddressStateOrProvince" xlink:to="lab_dei_EntityAddressStateOrProvince" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities_feacec0c-c0e3-43e0-9a1e-ae9c65e621a7_terseLabel_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-term debt and mandatorily redeemable securities</link:label>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities_3b461592-4792-4733-ad13-a90d338c773a_verboseLabel_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total long-term debt and mandatorily redeemable securities</link:label>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities_label_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long Term Debt and Mandatorily Redeemable Securities</link:label>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities_documentation_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents the aggregate carrying amount of long-term borrowings as of the balance sheet date including Federal Home Loan Bank borrowings, current portion of long term debt and promissory notes. Also includes the amount that is required to be paid, determined under the conditions specified in the contract, if as of the reporting date, the shares are mandatorily redeemable after one year from the reporting date or operating cycle, if longer.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:href="source-20211231.xsd#source_LongTermDebtAndMandatorilyRedeemableSecurities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:to="lab_source_LongTermDebtAndMandatorilyRedeemableSecurities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths_203f16e7-6a58-4819-8879-dcbf906ecfc9_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2022</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessor, Operating Lease, Payment to be Received, Year One</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets_528f1f56-dbca-4a5a-b49a-e36e49883a95_terseLabel_en-US" xlink:label="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Right of use assets - leases</link:label>
    <link:label id="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets_label_en-US" xlink:label="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Liabilities, Operating Lease Right of Use Assets</link:label>
    <link:label id="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets_documentation_en-US" xlink:label="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of deferred tax liability attributable to taxable temporary differences from operating lease right of use assets.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets" xlink:href="source-20211231.xsd#source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets" xlink:to="lab_source_DeferredTaxLiabilitiesOperatingLeaseRightofUseAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ReceivableTypeDomain_12a97284-f345-4412-ac95-cb1fe41b0edc_terseLabel_en-US" xlink:label="lab_us-gaap_ReceivableTypeDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Receivable Type [Domain]</link:label>
    <link:label id="lab_us-gaap_ReceivableTypeDomain_label_en-US" xlink:label="lab_us-gaap_ReceivableTypeDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Receivable [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ReceivableTypeDomain" xlink:to="lab_us-gaap_ReceivableTypeDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock_3d679f93-29f9-41d4-9e76-777e7201d2fd_terseLabel_en-US" xlink:label="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Summary of subordinated notes</link:label>
    <link:label id="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock_label_en-US" xlink:label="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Subordinated Notes Pertaining to Capital Trusts [Table Text Block]</link:label>
    <link:label id="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock_documentation_en-US" xlink:label="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tabular disclosure of junior subordinated notes issued to capital trusts including interest rates, maturity dates, original issuance and amount owed by issuance.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock" xlink:href="source-20211231.xsd#source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock" xlink:to="lab_source_ScheduleOfSubordinatedNotesPertainingToCapitalTrustsTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NonperformingFinancingReceivableMember_0a9647c5-0b00-4c99-9c41-1663a217a751_terseLabel_en-US" xlink:label="lab_us-gaap_NonperformingFinancingReceivableMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Nonperforming</link:label>
    <link:label id="lab_us-gaap_NonperformingFinancingReceivableMember_label_en-US" xlink:label="lab_us-gaap_NonperformingFinancingReceivableMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Nonperforming Financial Instruments [Member]</link:label>
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    <link:label id="lab_us-gaap_FairValueByBalanceSheetGroupingTextBlock_2a653568-87b2-40e5-8822-d6cfe48843b3_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of fair values of financial instruments</link:label>
    <link:label id="lab_us-gaap_FairValueByBalanceSheetGroupingTextBlock_label_en-US" xlink:label="lab_us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, by Balance Sheet Grouping [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:to="lab_us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherRealEstateAndForeclosedAssets_f7e42af3-db5b-4124-994f-2eb2eb9fd9e6_terseLabel_en-US" xlink:label="lab_us-gaap_OtherRealEstateAndForeclosedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Carrying value of other real estate</link:label>
    <link:label id="lab_us-gaap_OtherRealEstateAndForeclosedAssets_label_en-US" xlink:label="lab_us-gaap_OtherRealEstateAndForeclosedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Real Estate, Foreclosed Assets, and Repossessed Assets</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRealEstateAndForeclosedAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherRealEstateAndForeclosedAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherRealEstateAndForeclosedAssets" xlink:to="lab_us-gaap_OtherRealEstateAndForeclosedAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ServicingAssetFairValueExceedingCarryingValueAmount_e8c5bcc3-5d4d-4ba8-9267-c4b08e506764_terseLabel_en-US" xlink:label="lab_source_ServicingAssetFairValueExceedingCarryingValueAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair value of mortgage servicing rights exceeding the carrying value</link:label>
    <link:label id="lab_source_ServicingAssetFairValueExceedingCarryingValueAmount_label_en-US" xlink:label="lab_source_ServicingAssetFairValueExceedingCarryingValueAmount" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset Fair Value Exceeding Carrying Value Amount</link:label>
    <link:label id="lab_source_ServicingAssetFairValueExceedingCarryingValueAmount_documentation_en-US" xlink:label="lab_source_ServicingAssetFairValueExceedingCarryingValueAmount" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the difference between the fair value and carrying value of mortgage servicing assets.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ServicingAssetFairValueExceedingCarryingValueAmount" xlink:href="source-20211231.xsd#source_ServicingAssetFairValueExceedingCarryingValueAmount"/>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue_0aaccdfe-acbf-4568-b045-05d2d5daa9c0_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage-backed securities</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_source_StockOwnershipAndProfitSharingPlanMember_1ce079be-75a5-43a9-a6df-540de5a78895_terseLabel_en-US" xlink:label="lab_source_StockOwnershipAndProfitSharingPlanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employee Stock Ownership and Profit Sharing Plan</link:label>
    <link:label id="lab_source_StockOwnershipAndProfitSharingPlanMember_label_en-US" xlink:label="lab_source_StockOwnershipAndProfitSharingPlanMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock Ownership and Profit Sharing Plan [Member]</link:label>
    <link:label id="lab_source_StockOwnershipAndProfitSharingPlanMember_documentation_en-US" xlink:label="lab_source_StockOwnershipAndProfitSharingPlanMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to benefits payable to employees under Stock Ownership and Profit Sharing Plan.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_StockOwnershipAndProfitSharingPlanMember" xlink:href="source-20211231.xsd#source_StockOwnershipAndProfitSharingPlanMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_StockOwnershipAndProfitSharingPlanMember" xlink:to="lab_source_StockOwnershipAndProfitSharingPlanMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_6b50c386-1990-437f-9c8c-badebae22c20_terseLabel_en-US" xlink:label="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reclassification out of Accumulated Other Comprehensive Income [Axis]</link:label>
    <link:label id="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_label_en-US" xlink:label="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reclassification out of Accumulated Other Comprehensive Income [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:to="lab_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_IcfrAuditorAttestationFlag_e7d5af5b-800c-4bdc-aad7-c95e7ead32f2_terseLabel_en-US" xlink:label="lab_dei_IcfrAuditorAttestationFlag" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ICFR Auditor Attestation Flag</link:label>
    <link:label id="lab_dei_IcfrAuditorAttestationFlag_label_en-US" xlink:label="lab_dei_IcfrAuditorAttestationFlag" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ICFR Auditor Attestation Flag</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_IcfrAuditorAttestationFlag" xlink:to="lab_dei_IcfrAuditorAttestationFlag" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract_df38cc87-88d4-4851-9490-7eca2f1951d7_terseLabel_en-US" xlink:label="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Partnership investment</link:label>
    <link:label id="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract_label_en-US" xlink:label="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investments in and Advances to Affiliates, Balance [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract" xlink:to="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_68dfa900-fa44-4893-b1a4-9afe5c2672ee_terseLabel_en-US" xlink:label="lab_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contributions from noncontrolling interests</link:label>
    <link:label id="lab_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_label_en-US" xlink:label="lab_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noncontrolling Interest, Increase from Subsidiary Equity Issuance</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance" xlink:to="lab_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_8edecc24-8115-4ffa-9e8f-ebc329f87a57_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Summary of activity regarding active stock option and stock award plans</link:label>
    <link:label id="lab_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Payment Arrangement, Activity [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:to="lab_us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_TransferOtherRealEstateAndRepossessedAssets_d03b5c9c-5316-4a8b-9082-d5c08ecf5a59_terseLabel_en-US" xlink:label="lab_source_TransferOtherRealEstateAndRepossessedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans transferred to other real estate and repossessions</link:label>
    <link:label id="lab_source_TransferOtherRealEstateAndRepossessedAssets_label_en-US" xlink:label="lab_source_TransferOtherRealEstateAndRepossessedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfer Other Real Estate and Repossessed Assets</link:label>
    <link:label id="lab_source_TransferOtherRealEstateAndRepossessedAssets_documentation_en-US" xlink:label="lab_source_TransferOtherRealEstateAndRepossessedAssets" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents the value of real estate transferred in noncash transactions during the reporting period. Also includes repossessed assets.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_TransferOtherRealEstateAndRepossessedAssets" xlink:href="source-20211231.xsd#source_TransferOtherRealEstateAndRepossessedAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_TransferOtherRealEstateAndRepossessedAssets" xlink:to="lab_source_TransferOtherRealEstateAndRepossessedAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AntidilutiveSecuritiesNameDomain_a26f340d-0a4a-4f26-8b4d-4b7bdd074017_terseLabel_en-US" xlink:label="lab_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Antidilutive Securities, Name [Domain]</link:label>
    <link:label id="lab_us-gaap_AntidilutiveSecuritiesNameDomain_label_en-US" xlink:label="lab_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Antidilutive Securities, Name [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="lab_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_6b832c8d-c295-4719-bdcd-8cd8e671b234_terseLabel_en-US" xlink:label="lab_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment Securities</link:label>
    <link:label id="lab_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:to="lab_us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_9735c6a1-679f-4fe9-9d27-4c9ac5df1e06_terseLabel_en-US" xlink:label="lab_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Dilutive effect of stock compensation (in shares)</link:label>
    <link:label id="lab_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_label_en-US" xlink:label="lab_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:to="lab_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses_09faff74-3094-4eae-b5bd-69e3d56b42cf_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reserve for loan and lease losses</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Asset, Tax Deferred Expense, Reserve and Accrual, Financing Receivable, Allowance for Credit Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses" xlink:to="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestIncomeExpenseNet_b73154ad-4d6f-45a7-9e94-4bd94887d9e4_totalLabel_en-US" xlink:label="lab_us-gaap_InterestIncomeExpenseNet" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net interest income</link:label>
    <link:label id="lab_us-gaap_InterestIncomeExpenseNet_label_en-US" xlink:label="lab_us-gaap_InterestIncomeExpenseNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Income (Expense), Net</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestIncomeExpenseNet" xlink:to="lab_us-gaap_InterestIncomeExpenseNet" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward_23e10dde-fdbb-4c14-ad01-1236363ca342_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Changes in allowance for loan and lease losses</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward"/>
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    <link:label id="lab_us-gaap_DirectFinancingLeaseLeaseReceivable_0230f56d-983a-45d3-b8b4-aa35e3881049_terseLabel_en-US" xlink:label="lab_us-gaap_DirectFinancingLeaseLeaseReceivable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum lease payments</link:label>
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    <link:label id="lab_us-gaap_ProceedsFromSaleOfBuildings_a7fba69d-b1a4-443c-8bf0-7c3bfbaa9f84_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfBuildings" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from disposal of premises and equipment</link:label>
    <link:label id="lab_us-gaap_ProceedsFromSaleOfBuildings_label_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfBuildings" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from Sale of Buildings</link:label>
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    <link:label id="lab_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2_259797db-fc9d-4caa-b8a5-6cc6310b3748_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring, Postmodification</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring, Postmodification</link:label>
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    <link:label id="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock_d725f577-bf1b-4f8f-8a44-6dbf2a8da2eb_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of changes in Level 3 assets and liabilities measured at fair value on a recurring basis</link:label>
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    <link:label id="lab_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_c67e8974-5a3a-4876-8760-dff2b343d2cf_terseLabel_en-US" xlink:label="lab_us-gaap_ComprehensiveIncomeNetOfTaxAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other comprehensive income (loss):</link:label>
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    <link:label id="lab_us-gaap_CommonStockDividendsPerShareDeclared_76e40d7d-d328-4dba-9ffb-f8530d4205cf_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockDividendsPerShareDeclared" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock dividend (in dollars per share)</link:label>
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    <link:label id="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_fda35bc1-3127-444e-b395-acb7f5d60041_terseLabel_en-US" xlink:label="lab_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trust and wealth advisory, service charges on deposit accounts, and debit card income</link:label>
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    <link:label id="lab_source_SubordinatedNoteIssuedinAugust2007Member_b73875b2-fe57-459f-a3e4-2698d1bd7e71_terseLabel_en-US" xlink:label="lab_source_SubordinatedNoteIssuedinAugust2007Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">August 2007 issuance</link:label>
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    <link:label id="lab_us-gaap_OtherInterestAndDividendIncome_0087f1b8-71f8-47ae-96b1-bc6bf99e3686_terseLabel_en-US" xlink:label="lab_us-gaap_OtherInterestAndDividendIncome" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
    <link:label id="lab_us-gaap_OtherInterestAndDividendIncome_label_en-US" xlink:label="lab_us-gaap_OtherInterestAndDividendIncome" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Interest and Dividend Income</link:label>
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    <link:label id="lab_source_ProceedsFromDirectFinanceLeasePayments_2bf52bb7-0497-45d1-9b1f-c1d799bd3427_terseLabel_en-US" xlink:label="lab_source_ProceedsFromDirectFinanceLeasePayments" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from principal payments on direct finance leases</link:label>
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    <link:label id="lab_us-gaap_EmployeeStockOptionMember_0a9de2b3-7a3e-4785-a669-4785ac354456_terseLabel_en-US" xlink:label="lab_us-gaap_EmployeeStockOptionMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock options</link:label>
    <link:label id="lab_us-gaap_EmployeeStockOptionMember_label_en-US" xlink:label="lab_us-gaap_EmployeeStockOptionMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Payment Arrangement, Option [Member]</link:label>
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    <link:label id="lab_us-gaap_FairValueByFairValueHierarchyLevelAxis_8c5140aa-fc99-4e4d-87ad-af473e28d649_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Hierarchy and NAV [Axis]</link:label>
    <link:label id="lab_us-gaap_FairValueByFairValueHierarchyLevelAxis_label_en-US" xlink:label="lab_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Hierarchy and NAV [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
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    <link:label id="lab_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_5d52b2a4-1813-434f-9084-126d4b71ee93_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring [Table]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
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    <link:label id="lab_us-gaap_VariableRateAxis_da1236d9-c8b4-49fd-b210-ab2a65254d4f_terseLabel_en-US" xlink:label="lab_us-gaap_VariableRateAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Rate [Axis]</link:label>
    <link:label id="lab_us-gaap_VariableRateAxis_label_en-US" xlink:label="lab_us-gaap_VariableRateAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Rate [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_VariableRateAxis" xlink:to="lab_us-gaap_VariableRateAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets_2c4c2df3-b8d5-4d87-a28c-e5be8e64a691_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy Ratio (as a percent)</link:label>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets_label_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Tier One Leverage Capital Ratio, Capital Adequacy, Minimum</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets"/>
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    <link:label id="lab_us-gaap_FinancingReceivableModificationsRecordedInvestment_597c268a-bf3e-4dbd-b4b0-64b714307ffd_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsRecordedInvestment_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableModificationsRecordedInvestment"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:to="lab_us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:type="arc" order="1"/>
    <link:label id="lab_source_TimeDeposits250000orMore_ae467e94-2206-4615-b58c-c5f91eef04a9_totalLabel_en-US" xlink:label="lab_source_TimeDeposits250000orMore" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total</link:label>
    <link:label id="lab_source_TimeDeposits250000orMore_label_en-US" xlink:label="lab_source_TimeDeposits250000orMore" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Time Deposits, $250,000 or More</link:label>
    <link:label id="lab_source_TimeDeposits250000orMore_documentation_en-US" xlink:label="lab_source_TimeDeposits250000orMore" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_TimeDeposits250000orMore" xlink:href="source-20211231.xsd#source_TimeDeposits250000orMore"/>
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    <link:label id="lab_us-gaap_FinanceLoansAndLeasesReceivablePolicy_9c9b91b3-b50a-4fc6-805f-dc63f7c91987_terseLabel_en-US" xlink:label="lab_us-gaap_FinanceLoansAndLeasesReceivablePolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases</link:label>
    <link:label id="lab_us-gaap_FinanceLoansAndLeasesReceivablePolicy_label_en-US" xlink:label="lab_us-gaap_FinanceLoansAndLeasesReceivablePolicy" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLoansAndLeasesReceivablePolicy" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinanceLoansAndLeasesReceivablePolicy"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinanceLoansAndLeasesReceivablePolicy" xlink:to="lab_us-gaap_FinanceLoansAndLeasesReceivablePolicy" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommercialLoanMember_17a73266-43d2-4844-a74b-555c4e9256c1_terseLabel_en-US" xlink:label="lab_us-gaap_CommercialLoanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial loans</link:label>
    <link:label id="lab_us-gaap_CommercialLoanMember_label_en-US" xlink:label="lab_us-gaap_CommercialLoanMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial Loan [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialLoanMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialLoanMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommercialLoanMember" xlink:to="lab_us-gaap_CommercialLoanMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7585c55d-babc-4629-a3eb-3f4ee9072346_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Property, Plant and Equipment [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="lab_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f845b14d-521c-4374-9d86-cd5edbb1b739_terseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Increase (Decrease) in Stockholders' Equity</link:label>
    <link:label id="lab_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Increase (Decrease) in Stockholders' Equity [Roll Forward]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="lab_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_DocumentFiscalYearFocus_2e1c05d6-d726-4326-b69b-36a8d2ea076e_terseLabel_en-US" xlink:label="lab_dei_DocumentFiscalYearFocus" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Fiscal Year Focus</link:label>
    <link:label id="lab_dei_DocumentFiscalYearFocus_label_en-US" xlink:label="lab_dei_DocumentFiscalYearFocus" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Fiscal Year Focus</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentFiscalYearFocus"/>
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    <link:label id="lab_us-gaap_MeasurementInputConstantPrepaymentRateMember_f7781299-8dc1-4b77-a783-53999936795f_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputConstantPrepaymentRateMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Constant prepayment rate (CPR)</link:label>
    <link:label id="lab_us-gaap_MeasurementInputConstantPrepaymentRateMember_label_en-US" xlink:label="lab_us-gaap_MeasurementInputConstantPrepaymentRateMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Input, Constant Prepayment Rate [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputConstantPrepaymentRateMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MeasurementInputConstantPrepaymentRateMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MeasurementInputConstantPrepaymentRateMember" xlink:to="lab_us-gaap_MeasurementInputConstantPrepaymentRateMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_8289a2b3-28f1-4607-a4cb-ee4b900e4cb3_terseLabel_en-US" xlink:label="lab_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Forfeited (in shares)</link:label>
    <link:label id="lab_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_label_en-US" xlink:label="lab_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Shares Issued, Shares, Share-based Payment Arrangement, Forfeited</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited"/>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentAbstract_db706ce4-5463-4003-9d54-7911785406d5_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Premises and equipment</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentAbstract_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentAbstract" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers_6873da6d-592b-4a17-ae8f-4f6b21354790_terseLabel_en-US" xlink:label="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans sold or participated to others</link:label>
    <link:label id="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers_label_en-US" xlink:label="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from Loans Sold or Participated to Others</link:label>
    <link:label id="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers_documentation_en-US" xlink:label="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The cash inflow from held-for-investment loans sold or participated to others.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ProceedsFromLoansSoldOrParticipatedToOthers" xlink:href="source-20211231.xsd#source_ProceedsFromLoansSoldOrParticipatedToOthers"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ProceedsFromLoansSoldOrParticipatedToOthers" xlink:to="lab_source_ProceedsFromLoansSoldOrParticipatedToOthers" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ConstructionEquipmentFinancingMember_338f2202-b981-425d-a6e0-82b718983aab_terseLabel_en-US" xlink:label="lab_source_ConstructionEquipmentFinancingMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Construction equipment</link:label>
    <link:label id="lab_source_ConstructionEquipmentFinancingMember_label_en-US" xlink:label="lab_source_ConstructionEquipmentFinancingMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Construction Equipment Financing [Member]</link:label>
    <link:label id="lab_source_ConstructionEquipmentFinancingMember_documentation_en-US" xlink:label="lab_source_ConstructionEquipmentFinancingMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Portfolio segment of financing receivables related to construction equipment loans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ConstructionEquipmentFinancingMember" xlink:href="source-20211231.xsd#source_ConstructionEquipmentFinancingMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ConstructionEquipmentFinancingMember" xlink:to="lab_source_ConstructionEquipmentFinancingMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_VariableRateDomain_ec82ddc0-28cb-468f-8533-27999bb48b24_terseLabel_en-US" xlink:label="lab_us-gaap_VariableRateDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Rate [Domain]</link:label>
    <link:label id="lab_us-gaap_VariableRateDomain_label_en-US" xlink:label="lab_us-gaap_VariableRateDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Rate [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_VariableRateDomain" xlink:to="lab_us-gaap_VariableRateDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_ca180ee0-46cd-4ca0-a93f-8c2458513c46_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfers out of Level 3</link:label>
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    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesValueOfSharesToBePurchased_753b8d91-a725-40ec-b837-964422d6afa0_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesValueOfSharesToBePurchased" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Value of shares to be purchased</link:label>
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    <link:label id="lab_us-gaap_CollateralDomain_fb18320b-ac0a-478d-b918-c6ad5a728445_terseLabel_en-US" xlink:label="lab_us-gaap_CollateralDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral [Domain]</link:label>
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    <link:label id="lab_us-gaap_EquityMethodInvestmentsPolicy_4b295215-1ef7-424e-a819-9a8882fdb230_terseLabel_en-US" xlink:label="lab_us-gaap_EquityMethodInvestmentsPolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Partnership Investments</link:label>
    <link:label id="lab_us-gaap_EquityMethodInvestmentsPolicy_label_en-US" xlink:label="lab_us-gaap_EquityMethodInvestmentsPolicy" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity Method Investments [Policy Text Block]</link:label>
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    <link:label id="lab_us-gaap_RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock_4125d9ec-cd13-468a-9b22-805679c4169b_terseLabel_en-US" xlink:label="lab_us-gaap_RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Regulatory Matters</link:label>
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    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss_de114ce2-4aaf-49c0-bad2-72b3cb50713e_terseLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleAccruedInterestAfterAllowanceForCreditLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued interest receivable on investment securities available-for-sale</link:label>
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    <link:label id="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue_6ad6ab16-59a9-47eb-b1c9-69ff9457cbfc_terseLabel_en-US" xlink:label="lab_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment in partnership</link:label>
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    <link:label id="lab_us-gaap_TierOneRiskBasedCapitalAbstract_295315d9-118e-4577-8df1-58f767673c5d_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneRiskBasedCapitalAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tier I Capital (to Risk-Weighted Assets):</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfServicingAssetsAtAmortizedValueTextBlock_a38e8a0a-e810-4ffd-8d03-e75fdbfea632_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfServicingAssetsAtAmortizedValueTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of changes in carrying value of mortgage servicing rights and the associated valuation allowance</link:label>
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    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPremiumFromMarketPriceOfferingDate_1eb977e6-1284-435e-925d-7b005c6ddc6d_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPremiumFromMarketPriceOfferingDate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Percentage of the premium fair market value of common stock as on the offering date or the market value as on the purchase date (as a percent)</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPremiumFromMarketPriceOfferingDate_label_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPremiumFromMarketPriceOfferingDate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share Based Compensation Arrangement By Share Based Payment Award Premium From Market Price Offering Date</link:label>
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    <link:label id="lab_source_LoansAndLeasesReceivableEvaluatedForImpairment_73b6c63f-da22-456a-a06b-94f946b15b4b_terseLabel_en-US" xlink:label="lab_source_LoansAndLeasesReceivableEvaluatedForImpairment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Threshold value of loan or lease for evaluation of the appropriateness of the impairment reserve</link:label>
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    <link:label id="lab_srt_MaximumMember_ce1a3d4d-45b5-4b0e-863f-75881ed93336_terseLabel_en-US" xlink:label="lab_srt_MaximumMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maximum</link:label>
    <link:label id="lab_srt_MaximumMember_label_en-US" xlink:label="lab_srt_MaximumMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maximum [Member]</link:label>
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    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_7aec0f82-f929-45b6-81cf-df7f37bf6bd6_terseLabel_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reasons for the difference between income tax expense rate and statutory federal income tax rate</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:to="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_b11eb876-a5d2-4b51-9c57-e5d6189a1b2e_terseLabel_en-US" xlink:label="lab_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Payment Arrangement [Abstract]</link:label>
    <link:label id="lab_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_label_en-US" xlink:label="lab_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Payment Arrangement [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:to="lab_us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_AuditInformationAbstract_label_en-US" xlink:label="lab_source_AuditInformationAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Audit Information [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_AuditInformationAbstract" xlink:href="source-20211231.xsd#source_AuditInformationAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_AuditInformationAbstract" xlink:to="lab_source_AuditInformationAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare_38a953de-264f-4b06-a0f6-5b210b3cf602_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Purchases price (in dollars per share)</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare_label_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share Based Compensation Arrangement by Share Based Payment Award, Price Per Share</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare_documentation_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents price per share for shares which will be issued to employees under the plan.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare" xlink:href="source-20211231.xsd#source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare" xlink:to="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPricePerShare" xlink:type="arc" order="1"/>
    <link:label id="lab_source_IncreaseDecreaseinSavingandDemandDeposits_05c32ba4-9a80-4fa2-a461-fd81aed1ba92_terseLabel_en-US" xlink:label="lab_source_IncreaseDecreaseinSavingandDemandDeposits" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in demand deposits and savings accounts</link:label>
    <link:label id="lab_source_IncreaseDecreaseinSavingandDemandDeposits_label_en-US" xlink:label="lab_source_IncreaseDecreaseinSavingandDemandDeposits" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Increase (Decrease) in Saving and Demand Deposits</link:label>
    <link:label id="lab_source_IncreaseDecreaseinSavingandDemandDeposits_documentation_en-US" xlink:label="lab_source_IncreaseDecreaseinSavingandDemandDeposits" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents the net cash inflow (outflow) in the total of all savings account deposits and demand deposit accounts classified as cash flows from financing activities.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_IncreaseDecreaseinSavingandDemandDeposits" xlink:href="source-20211231.xsd#source_IncreaseDecreaseinSavingandDemandDeposits"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_IncreaseDecreaseinSavingandDemandDeposits" xlink:to="lab_source_IncreaseDecreaseinSavingandDemandDeposits" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AwardTypeAxis_6f39eb05-4d04-49b3-96e1-d6944a8cb4ae_terseLabel_en-US" xlink:label="lab_us-gaap_AwardTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Award Type [Axis]</link:label>
    <link:label id="lab_us-gaap_AwardTypeAxis_label_en-US" xlink:label="lab_us-gaap_AwardTypeAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Award Type [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AwardTypeAxis" xlink:to="lab_us-gaap_AwardTypeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_f53a07dc-6217-4cb6-8a17-90e6b6106a7a_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Future minimum rental commitments for noncancellable operating leases</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, Maturity [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StockholdersEquity_c67065b5-4ad5-487d-b4e1-2fbd31b6028d_totalLabel_en-US" xlink:label="lab_us-gaap_StockholdersEquity" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total shareholders&#8217; equity</link:label>
    <link:label id="lab_us-gaap_StockholdersEquity_326b39e7-b990-48a1-bf3d-77739e100fc1_terseLabel_en-US" xlink:label="lab_us-gaap_StockholdersEquity" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total shareholders&#8217; equity</link:label>
    <link:label id="lab_us-gaap_StockholdersEquity_label_en-US" xlink:label="lab_us-gaap_StockholdersEquity" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stockholders' Equity Attributable to Parent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StockholdersEquity" xlink:to="lab_us-gaap_StockholdersEquity" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShorttermDebtFairValue_841dbab9-9b9a-449a-b5f0-2134f81042fc_terseLabel_en-US" xlink:label="lab_us-gaap_ShorttermDebtFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term borrowings</link:label>
    <link:label id="lab_us-gaap_ShorttermDebtFairValue_label_en-US" xlink:label="lab_us-gaap_ShorttermDebtFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt, Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShorttermDebtFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShorttermDebtFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShorttermDebtFairValue" xlink:to="lab_us-gaap_ShorttermDebtFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TimeDepositsByMaturityAbstract_c5503099-be52-4d75-8055-571c68c1b3fb_terseLabel_en-US" xlink:label="lab_us-gaap_TimeDepositsByMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maturities of time deposits, including both private and public funds</link:label>
    <link:label id="lab_us-gaap_TimeDepositsByMaturityAbstract_label_en-US" xlink:label="lab_us-gaap_TimeDepositsByMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Time Deposits, Fiscal Year Maturity [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDepositsByMaturityAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TimeDepositsByMaturityAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TimeDepositsByMaturityAbstract" xlink:to="lab_us-gaap_TimeDepositsByMaturityAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DepositAccountMember_3aea0335-47b5-4c7d-bc76-82b5634fd2d3_terseLabel_en-US" xlink:label="lab_us-gaap_DepositAccountMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Service charges on deposit accounts</link:label>
    <link:label id="lab_us-gaap_DepositAccountMember_label_en-US" xlink:label="lab_us-gaap_DepositAccountMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deposit Account [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositAccountMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DepositAccountMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DepositAccountMember" xlink:to="lab_us-gaap_DepositAccountMember" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_CityAreaCode_2e590ed0-fb47-42b7-ad3e-f4786e4701ec_terseLabel_en-US" xlink:label="lab_dei_CityAreaCode" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">City Area Code</link:label>
    <link:label id="lab_dei_CityAreaCode_label_en-US" xlink:label="lab_dei_CityAreaCode" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">City Area Code</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_CityAreaCode"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_CityAreaCode" xlink:to="lab_dei_CityAreaCode" xlink:type="arc" order="1"/>
    <link:label id="lab_source_MediumAndHeavyDutyTrucksMember_acfe38ae-47c7-4beb-9a35-8c8619d5b770_terseLabel_en-US" xlink:label="lab_source_MediumAndHeavyDutyTrucksMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Medium and heavy duty trucks</link:label>
    <link:label id="lab_source_MediumAndHeavyDutyTrucksMember_label_en-US" xlink:label="lab_source_MediumAndHeavyDutyTrucksMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Medium and Heavy Duty Trucks [Member]</link:label>
    <link:label id="lab_source_MediumAndHeavyDutyTrucksMember_documentation_en-US" xlink:label="lab_source_MediumAndHeavyDutyTrucksMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to medium and heavy duty trucks.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_MediumAndHeavyDutyTrucksMember" xlink:href="source-20211231.xsd#source_MediumAndHeavyDutyTrucksMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_MediumAndHeavyDutyTrucksMember" xlink:to="lab_source_MediumAndHeavyDutyTrucksMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CommonStockEarningsLossBasic_0ae3b5ec-917f-45dc-bc40-18d7c4c13259_terseLabel_en-US" xlink:label="lab_source_CommonStockEarningsLossBasic" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net earnings allocated to common stock</link:label>
    <link:label id="lab_source_CommonStockEarningsLossBasic_label_en-US" xlink:label="lab_source_CommonStockEarningsLossBasic" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Stock Earnings (Loss), Basic</link:label>
    <link:label id="lab_source_CommonStockEarningsLossBasic_documentation_en-US" xlink:label="lab_source_CommonStockEarningsLossBasic" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of earnings (loss) allocated to common stock for the basic earnings (loss) per share or per unit calculation under the two-class method.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CommonStockEarningsLossBasic" xlink:href="source-20211231.xsd#source_CommonStockEarningsLossBasic"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CommonStockEarningsLossBasic" xlink:to="lab_source_CommonStockEarningsLossBasic" xlink:type="arc" order="1"/>
    <link:label id="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans_fa0181ee-ecbc-41db-82ca-07c2a23a4b39_terseLabel_en-US" xlink:label="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total Accruing Loans</link:label>
    <link:label id="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans_label_en-US" xlink:label="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable Recorded Investment Accruing Loans</link:label>
    <link:label id="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans_documentation_en-US" xlink:label="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents recorded investment in financing receivables that are accruing.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_FinancingReceivableRecordedInvestmentAccruingLoans" xlink:href="source-20211231.xsd#source_FinancingReceivableRecordedInvestmentAccruingLoans"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_FinancingReceivableRecordedInvestmentAccruingLoans" xlink:to="lab_source_FinancingReceivableRecordedInvestmentAccruingLoans" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CapitalAbstract_9dbde4a9-3827-4566-bd9b-4d8cfcde4267_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total Capital (to Risk-Weighted Assets):</link:label>
    <link:label id="lab_us-gaap_CapitalAbstract_label_en-US" xlink:label="lab_us-gaap_CapitalAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Total Capital [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CapitalAbstract" xlink:to="lab_us-gaap_CapitalAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_6f1c17a8-4c7d-4f6a-ae8f-3c72ab4a4d9c_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill and intangibles</link:label>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_label_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill and Intangible Assets Disclosure [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:to="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_601cd335-51d3-4aa8-82ee-42d2387f715b_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total gains or losses (unrealized): included in earnings</link:label>
    <link:label id="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_label_en-US" xlink:label="lab_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)</link:label>
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    <link:label id="lab_us-gaap_IncreaseDecreaseInTimeDeposits_11cf6bb6-80b5-4cf6-93b1-f9bf431b43e6_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInTimeDeposits" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in time deposits</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue_cabdaed7-064b-4321-851f-faf37d5c982b_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Due after one year through five years</link:label>
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    <link:label id="lab_source_FederalFundsSoldAndInterestBearingDepositsInBanks_1c602462-a352-4296-b387-eb54eeeebe04_terseLabel_en-US" xlink:label="lab_source_FederalFundsSoldAndInterestBearingDepositsInBanks" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal funds sold and interest bearing deposits with other banks</link:label>
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    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedNextTwelveMonths_f002c80b-e616-428a-9de2-38a6ccad3e63_terseLabel_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2022</link:label>
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    <link:label id="lab_source_ForwardContractsMortgageLoanMember_ab2952a2-92c1-4922-b21d-a7d490b097dc_terseLabel_en-US" xlink:label="lab_source_ForwardContractsMortgageLoanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Forward contracts - mortgage loan</link:label>
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    <link:label id="lab_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_a3899d7c-51c1-4f23-8eb5-ea412064142b_terseLabel_en-US" xlink:label="lab_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income tax benefit due to stock-based compensation expenses</link:label>
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    <link:label id="lab_us-gaap_FairValueByBalanceSheetGroupingTable_label_en-US" xlink:label="lab_us-gaap_FairValueByBalanceSheetGroupingTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, by Balance Sheet Grouping [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_45d13060-904c-48b0-ba93-24f359102a25_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing activities:</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract"/>
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    <link:label id="lab_us-gaap_DerivativeInstrumentsGainLossLineItems_f6f084af-a524-46a9-bde0-3ceac5d1f97d_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Financial Instruments</link:label>
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    <link:label id="lab_source_ScheduleofComponentsofLeaseInvestmentsbyCategoryTableTextBlock_0e0112b5-7655-4a34-909c-8b6984d3444a_terseLabel_en-US" xlink:label="lab_source_ScheduleofComponentsofLeaseInvestmentsbyCategoryTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of components of lease investments by category</link:label>
    <link:label id="lab_source_ScheduleofComponentsofLeaseInvestmentsbyCategoryTableTextBlock_label_en-US" xlink:label="lab_source_ScheduleofComponentsofLeaseInvestmentsbyCategoryTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Components of Lease Investments by Category [Table Text Block]</link:label>
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    <link:label id="lab_us-gaap_FederalFundsPurchasedMember_522504af-3022-45cc-a198-68dd329d239e_terseLabel_en-US" xlink:label="lab_us-gaap_FederalFundsPurchasedMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal funds purchased</link:label>
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    <link:label id="lab_us-gaap_EquityComponentDomain_7e33056f-aa40-42c7-9ca0-e128033d1346_terseLabel_en-US" xlink:label="lab_us-gaap_EquityComponentDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity Component [Domain]</link:label>
    <link:label id="lab_us-gaap_EquityComponentDomain_label_en-US" xlink:label="lab_us-gaap_EquityComponentDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity Component [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="lab_us-gaap_EquityComponentDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SaleAndLeasebackTransactionGainLossNet_e212b3ca-9701-4bf9-a4e2-cf169730b58c_terseLabel_en-US" xlink:label="lab_us-gaap_SaleAndLeasebackTransactionGainLossNet" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net gain on sale of building with a subsequent operating lease</link:label>
    <link:label id="lab_us-gaap_SaleAndLeasebackTransactionGainLossNet_label_en-US" xlink:label="lab_us-gaap_SaleAndLeasebackTransactionGainLossNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Sale and Leaseback Transaction, Gain (Loss), Net</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SaleAndLeasebackTransactionGainLossNet" xlink:to="lab_us-gaap_SaleAndLeasebackTransactionGainLossNet" xlink:type="arc" order="1"/>
    <link:label id="lab_source_AutoAndLightTruckMember_036dd0c3-0e47-4ead-a40f-d93592fc1a9d_terseLabel_en-US" xlink:label="lab_source_AutoAndLightTruckMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auto and light truck</link:label>
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    <link:label id="lab_source_AutoAndLightTruckMember_documentation_en-US" xlink:label="lab_source_AutoAndLightTruckMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Class of financing receivables related to auto and light truck loans.</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_6ee82727-887b-4213-8ab5-63c351cbfca1_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2022</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, Year One</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_67976273-be8c-4acf-bb47-b96a3a244c4c_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Accounts, Notes, Loans and Financing Receivable [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Accounts, Notes, Loans and Financing Receivable [Table]</link:label>
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    <link:label id="lab_us-gaap_ComponentsOfDeferredTaxAssetsAbstract_2ca9b1b9-4059-4b87-8c9e-813c61c81858_terseLabel_en-US" xlink:label="lab_us-gaap_ComponentsOfDeferredTaxAssetsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred tax assets:</link:label>
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    <link:label id="lab_source_TradePublicationsAndAuctionValuesValuationTechniqueMember_f6bd88d0-c7fe-4383-ae12-44bda3f423f8_terseLabel_en-US" xlink:label="lab_source_TradePublicationsAndAuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trade publications and auction values</link:label>
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    <link:label id="lab_source_TradePublicationsAndAuctionValuesValuationTechniqueMember_documentation_en-US" xlink:label="lab_source_TradePublicationsAndAuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents trade publications and auction values valuation technique used to measure fair value.</link:label>
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    <link:label id="lab_us-gaap_SubordinatedBorrowingAxis_9ac769bc-f57a-4367-b7cf-08144ddbf121_terseLabel_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated Borrowing [Axis]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedBorrowingAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedBorrowingAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SubordinatedBorrowingAxis" xlink:to="lab_us-gaap_SubordinatedBorrowingAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommercialPaper_65b518a4-67ee-488b-a5f5-1c29c46be7bc_terseLabel_en-US" xlink:label="lab_us-gaap_CommercialPaper" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial paper</link:label>
    <link:label id="lab_us-gaap_CommercialPaper_label_en-US" xlink:label="lab_us-gaap_CommercialPaper" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial Paper</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommercialPaper" xlink:to="lab_us-gaap_CommercialPaper" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShortTermDebtTypeAxis_028fc544-6afc-4ed4-912d-0b9570f181b5_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermDebtTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt, Type [Axis]</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesAbstract_585d3b25-d2ef-4c82-8cb1-283de75b11b5_terseLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">LIABILITIES</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LiabilitiesAbstract" xlink:to="lab_us-gaap_LiabilitiesAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm_7593063e-bb8b-4acf-bfd1-c5730ed64620_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual life</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm_label_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share Based Compensation Arrangements by Share Based Payment Award, Options Expiration Term</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm_documentation_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The period of time, from the grant date until the time at which the share-based [option] award expires.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:href="source-20211231.xsd#source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:to="lab_source_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SubordinatedBorrowingInterestRate_cda686f5-72e0-4eb3-9e6a-ef0150994cac_terseLabel_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingInterestRate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Rate (as a percent)</link:label>
    <link:label id="lab_us-gaap_SubordinatedBorrowingInterestRate_label_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingInterestRate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated Borrowing, Interest Rate</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedBorrowingInterestRate" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedBorrowingInterestRate"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SubordinatedBorrowingInterestRate" xlink:to="lab_us-gaap_SubordinatedBorrowingInterestRate" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_86396256-e66d-413d-bd71-a3a1f84f3d6f_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2025</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, Year Four</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems_5d28718d-a39f-4235-942a-09110fd0e6c6_terseLabel_en-US" xlink:label="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule Of Available For Sale Debt Securities [Line Items]</link:label>
    <link:label id="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems_label_en-US" xlink:label="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule Of Available For Sale Debt Securities [Line Items]</link:label>
    <link:label id="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems_documentation_en-US" xlink:label="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">[Line Items] for Schedule Of Available For Sale Debt Securities [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems" xlink:href="source-20211231.xsd#source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems" xlink:to="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_WeightedAverageMember_defa35d9-be1a-40c0-bdb8-7594e9bad7cc_terseLabel_en-US" xlink:label="lab_srt_WeightedAverageMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Weighted Average [Member]</link:label>
    <link:label id="lab_srt_WeightedAverageMember_label_en-US" xlink:label="lab_srt_WeightedAverageMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Weighted Average [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_WeightedAverageMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_WeightedAverageMember" xlink:to="lab_srt_WeightedAverageMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross_d65e8c1f-e636-44f4-a907-4b590cc0b13e_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net unrealized losses on securities available-for-sale</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Asset, Debt Securities, Available-for-Sale, Unrealized Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross" xlink:to="lab_us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueInputsLevel2Member_97a5b854-d7be-4164-bfba-629b805ad81d_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueInputsLevel2Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Level 2</link:label>
    <link:label id="lab_us-gaap_FairValueInputsLevel2Member_label_en-US" xlink:label="lab_us-gaap_FairValueInputsLevel2Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Inputs, Level 2 [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueInputsLevel2Member" xlink:to="lab_us-gaap_FairValueInputsLevel2Member" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_AuditorLocation_5056a08f-1979-4901-972a-4a2a0799649b_terseLabel_en-US" xlink:label="lab_dei_AuditorLocation" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auditor Location</link:label>
    <link:label id="lab_dei_AuditorLocation_label_en-US" xlink:label="lab_dei_AuditorLocation" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auditor Location</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AuditorLocation" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_AuditorLocation"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_AuditorLocation" xlink:to="lab_dei_AuditorLocation" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic_b3810d9c-452e-4b60-9a22-35df644121ff_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net earnings allocated to participating securities</link:label>
    <link:label id="lab_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic_label_en-US" xlink:label="lab_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Participating Securities, Distributed and Undistributed Earnings (Loss), Basic</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic" xlink:to="lab_us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeGainLossOnDerivativeNet_73b607da-a3c1-44c2-9eff-0ff342aaf310_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeGainLossOnDerivativeNet" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gain (loss)</link:label>
    <link:label id="lab_us-gaap_DerivativeGainLossOnDerivativeNet_label_en-US" xlink:label="lab_us-gaap_DerivativeGainLossOnDerivativeNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative, Gain (Loss) on Derivative, Net</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeGainLossOnDerivativeNet" xlink:to="lab_us-gaap_DerivativeGainLossOnDerivativeNet" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_f1b5d541-56ee-433d-a254-cacb03f6dc48_totalLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total fair value</link:label>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_label_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Unrealized Loss Position</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:to="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableRecordedInvestmentLineItems_585b16aa-33b2-445c-b3e8-17ff613ed848_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan and Lease Financings</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableRecordedInvestmentLineItems_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Credit Quality Indicator [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="lab_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SegmentReportingAbstract_6cea43c7-a851-4194-bb5e-281741b6c388_terseLabel_en-US" xlink:label="lab_us-gaap_SegmentReportingAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Segment reporting</link:label>
    <link:label id="lab_us-gaap_SegmentReportingAbstract_label_en-US" xlink:label="lab_us-gaap_SegmentReportingAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Segment Reporting [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentReportingAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SegmentReportingAbstract" xlink:to="lab_us-gaap_SegmentReportingAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ImpairedLoansMember_5546d1a5-ec6b-4e48-a53c-64ea40634b9f_terseLabel_en-US" xlink:label="lab_source_ImpairedLoansMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral-dependent impaired loans</link:label>
    <link:label id="lab_source_ImpairedLoansMember_label_en-US" xlink:label="lab_source_ImpairedLoansMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impaired Loans [Member]</link:label>
    <link:label id="lab_source_ImpairedLoansMember_documentation_en-US" xlink:label="lab_source_ImpairedLoansMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Details pertaining to loans impaired.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ImpairedLoansMember" xlink:href="source-20211231.xsd#source_ImpairedLoansMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ImpairedLoansMember" xlink:to="lab_source_ImpairedLoansMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_08559a88-a2a8-4d95-b4d0-c2d65e4bba53_totalLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total debt securities available-for-sale</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Amortized Cost</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:to="lab_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetUsefulLife_ba5c849d-edec-42c8-9a32-8af91a85be00_terseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Useful life of finite lived assets</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetUsefulLife_label_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Asset, Useful Life</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:to="lab_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CashAndDueFromBanksExcludingFederalHomeLoanBankCashFairValueDisclosure_c1b3ce46-a790-4e53-b885-04e41936e094_terseLabel_en-US" xlink:label="lab_source_CashAndDueFromBanksExcludingFederalHomeLoanBankCashFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and due from banks</link:label>
    <link:label id="lab_source_CashAndDueFromBanksExcludingFederalHomeLoanBankCashFairValueDisclosure_label_en-US" xlink:label="lab_source_CashAndDueFromBanksExcludingFederalHomeLoanBankCashFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and Due from Banks Excluding Federal Home Loan Bank Cash Fair Value Disclosure</link:label>
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    <link:label id="lab_us-gaap_CapitalRequiredForCapitalAdequacy_e18cee12-d307-4f47-bb7a-1fa3e053c208_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalRequiredForCapitalAdequacy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy Amount</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_249e162c-0134-4f56-91ba-56a66af57044_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of reconciliation of the number of shares used in the calculation of basic and diluted earnings per common share</link:label>
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    <link:label id="lab_us-gaap_InterestIncomeSecuritiesTaxExempt_bf286079-5111-4525-bd1f-27a6038ca30a_terseLabel_en-US" xlink:label="lab_us-gaap_InterestIncomeSecuritiesTaxExempt" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment securities, tax-exempt</link:label>
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    <link:label id="lab_source_SummaryOfSignificantAccountingPoliciesTable_6e358066-cb47-4aa1-bed1-7cee0124e0ea_terseLabel_en-US" xlink:label="lab_source_SummaryOfSignificantAccountingPoliciesTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Summary of Significant Accounting Policies [Table]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_source_SummaryOfSignificantAccountingPoliciesTable" xlink:href="source-20211231.xsd#source_SummaryOfSignificantAccountingPoliciesTable"/>
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    <link:label id="lab_us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral_3ed643ac-de67-4c6c-b236-822af47ba3d7_totalLabel_en-US" xlink:label="lab_us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Amount</link:label>
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    <link:label id="lab_us-gaap_DirectFinancingLeaseInterestIncome_bfb62785-3f20-4264-80df-45d5e2e04ba0_terseLabel_en-US" xlink:label="lab_us-gaap_DirectFinancingLeaseInterestIncome" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest income on lease receivable</link:label>
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    <link:label id="lab_dei_Security12bTitle_96786e36-7550-4d63-a135-8e4878e59eb3_terseLabel_en-US" xlink:label="lab_dei_Security12bTitle" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Title of 12(b) Security</link:label>
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    <link:label id="lab_us-gaap_FairValueOptionQuantitativeDisclosuresTextBlock_78ccf237-b354-413a-ab28-f9dc51c10449_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueOptionQuantitativeDisclosuresTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of differences between the fair value carrying amount of mortgages held for sale measured at fair value and the aggregate unpaid principal amount</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost_c877c3a0-5613-43ab-8504-7805897eaee1_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage-backed securities</link:label>
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    <link:label id="lab_us-gaap_ShortTermBorrowingsAbstract_2bea816b-1886-4d08-8dc6-d2859d24153a_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermBorrowingsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term borrowings:</link:label>
    <link:label id="lab_us-gaap_ShortTermBorrowingsAbstract_label_en-US" xlink:label="lab_us-gaap_ShortTermBorrowingsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowingsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShortTermBorrowingsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract" xlink:to="lab_us-gaap_ShortTermBorrowingsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherRealEstateOwnedMeasurementInput_51bd7fff-7d44-4f5a-b3f3-1673bb77fc87_terseLabel_en-US" xlink:label="lab_us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other real estate unobservable inputs (as a percent)</link:label>
    <link:label id="lab_us-gaap_OtherRealEstateOwnedMeasurementInput_label_en-US" xlink:label="lab_us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Real Estate Owned, Measurement Input</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherRealEstateOwnedMeasurementInput"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:to="lab_us-gaap_OtherRealEstateOwnedMeasurementInput" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets_0d3e7a21-35af-4306-9d55-1710e019bd6c_terseLabel_en-US" xlink:label="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy with Capital Buffer Ratio (as a percent)</link:label>
    <link:label id="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets_label_en-US" xlink:label="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets</link:label>
    <link:label id="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets_documentation_en-US" xlink:label="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The minimum Total risk based capital ratio (total capital divided by risk weighted assets required for capital adequacy with capital buffer purposes under the regulatory framework for prompt corrective action.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:href="source-20211231.xsd#source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:to="lab_source_CapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_8106d4ae-218d-4c9b-a161-20a552db1d0d_totalLabel_en-US" xlink:label="lab_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net income available to common shareholders</link:label>
    <link:label id="lab_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_label_en-US" xlink:label="lab_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Income (Loss) Available to Common Stockholders, Basic</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:to="lab_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_DocumentType_49fa7ea8-9c6a-4770-a7d8-dd1e6535428f_terseLabel_en-US" xlink:label="lab_dei_DocumentType" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Type</link:label>
    <link:label id="lab_dei_DocumentType_label_en-US" xlink:label="lab_dei_DocumentType" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Type</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentType"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_DocumentType" xlink:to="lab_dei_DocumentType" xlink:type="arc" order="1"/>
    <link:label id="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_fa64aca3-aa50-4443-8c7d-42f940689055_terseLabel_en-US" xlink:label="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maturity date of subordinated notes</link:label>
    <link:label id="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_label_en-US" xlink:label="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maturity Date of Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust</link:label>
    <link:label id="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_documentation_en-US" xlink:label="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maturity date of junior subordinated long-term debt owed to unconsolidated subsidiary trusts.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:href="source-20211231.xsd#source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:to="lab_source_MaturityDateOfJuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_ProductsAndServicesDomain_1784918f-26f3-4b44-81c6-a199608703d0_terseLabel_en-US" xlink:label="lab_srt_ProductsAndServicesDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Product and Service [Domain]</link:label>
    <link:label id="lab_srt_ProductsAndServicesDomain_label_en-US" xlink:label="lab_srt_ProductsAndServicesDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Product and Service [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_ProductsAndServicesDomain" xlink:to="lab_srt_ProductsAndServicesDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember_764e32af-0841-41e6-8070-b546bf8ef0f7_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Discount for lack of marketability</link:label>
    <link:label id="lab_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember_label_en-US" xlink:label="lab_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Input, Discount for Lack of Marketability [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember" xlink:to="lab_us-gaap_MeasurementInputDiscountForLackOfMarketabilityMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SubordinatedBorrowingTable_518be88a-d13e-416e-ab6c-4db1dfac4483_terseLabel_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated Borrowing [Table]</link:label>
    <link:label id="lab_us-gaap_SubordinatedBorrowingTable_label_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated Borrowing [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedBorrowingTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedBorrowingTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SubordinatedBorrowingTable" xlink:to="lab_us-gaap_SubordinatedBorrowingTable" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess_e1ad52fe-d139-4f72-a74d-62504bedb2e2_terseLabel_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Under 3 months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess_label_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual Maturities, Time Deposits, $250,000 or More, Three Months or Less</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess_documentation_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The amount of contractual maturities of domestic and foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more, for three months or less from the balance sheet date.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess" xlink:href="source-20211231.xsd#source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess" xlink:to="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsorLess" xlink:type="arc" order="1"/>
    <link:label id="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral_c68af5be-d4fb-4dc5-90cc-0c9c7d5a1600_terseLabel_en-US" xlink:label="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Period of amortization to reach equity position in collateral</link:label>
    <link:label id="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral_label_en-US" xlink:label="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PeriodOfAmortizationToReachEquityPositionInCollateral</link:label>
    <link:label id="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral_documentation_en-US" xlink:label="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Period of amortization to reach equity position in collateral</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_PeriodOfAmortizationToReachEquityPositionInCollateral" xlink:href="source-20211231.xsd#source_PeriodOfAmortizationToReachEquityPositionInCollateral"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_PeriodOfAmortizationToReachEquityPositionInCollateral" xlink:to="lab_source_PeriodOfAmortizationToReachEquityPositionInCollateral" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_9f679ae0-7c33-4b28-bb1f-dad6fe677258_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2023</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessor, Operating Lease, Payment to be Received, Year Two</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearFive_671cc88e-38ff-4c67-874e-317c65a1b3d5_terseLabel_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2026</link:label>
    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearFive_label_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearFive" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Time Deposit Maturities, Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDepositMaturitiesYearFive" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TimeDepositMaturitiesYearFive"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TimeDepositMaturitiesYearFive" xlink:to="lab_us-gaap_TimeDepositMaturitiesYearFive" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_43d785f9-09ed-42b6-af33-06e805fa0b1d_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Thereafter</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessor, Operating Lease, Payment to be Received, after Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueInputsQuantitativeInformationAbstract_f6acb570-e001-4385-bcc6-501dfd0009fa_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unobservable Inputs</link:label>
    <link:label id="lab_us-gaap_FairValueInputsQuantitativeInformationAbstract_label_en-US" xlink:label="lab_us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Measurement Inputs and Valuation Techniques [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsQuantitativeInformationAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:to="lab_us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommonEquityTierOneCapitalAbstract_62032762-4914-4852-98ed-b75c57095c5a_terseLabel_en-US" xlink:label="lab_us-gaap_CommonEquityTierOneCapitalAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Equity Tier 1 Capital (to Risk-Weighted Assets):</link:label>
    <link:label id="lab_us-gaap_CommonEquityTierOneCapitalAbstract_label_en-US" xlink:label="lab_us-gaap_CommonEquityTierOneCapitalAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Common Equity Tier One Risk-Based Capital [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonEquityTierOneCapitalAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonEquityTierOneCapitalAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommonEquityTierOneCapitalAbstract" xlink:to="lab_us-gaap_CommonEquityTierOneCapitalAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_f33af720-617c-47f1-92af-2aac89ff5dca_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net (income) loss attributable to noncontrolling interests</link:label>
    <link:label id="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_label_en-US" xlink:label="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Income (Loss) Attributable to Noncontrolling Interest</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:to="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax_51e71daa-45f8-4fe9-b73e-b4177443bcd4_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reclassification adjustment for realized losses (gains) included in net income</link:label>
    <link:label id="lab_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax_label_en-US" xlink:label="lab_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax" xlink:to="lab_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract_6a322eab-3531-4235-83ba-c5098cf65e59_terseLabel_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expected amortization expense on mortgage servicing rights</link:label>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract_label_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Value Expected Amortization [Abstract]</link:label>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract_documentation_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract" xlink:href="source-20211231.xsd#source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract" xlink:to="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f7443544-5143-4663-804e-26dd1485cf9c_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock-based compensation</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueByMeasurementFrequencyAxis_90fa74ab-4812-4adc-8b86-9b30babbe381_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Frequency [Axis]</link:label>
    <link:label id="lab_us-gaap_FairValueByMeasurementFrequencyAxis_label_en-US" xlink:label="lab_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Frequency [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="lab_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NoninterestIncome_f0b09248-ed93-4927-8f0c-b1977ec4abdc_totalLabel_en-US" xlink:label="lab_us-gaap_NoninterestIncome" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total noninterest income</link:label>
    <link:label id="lab_us-gaap_NoninterestIncome_label_en-US" xlink:label="lab_us-gaap_NoninterestIncome" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noninterest Income</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncome" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoninterestIncome"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NoninterestIncome" xlink:to="lab_us-gaap_NoninterestIncome" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LeaseCostTableTextBlock_6e7ef641-0ca0-4d7d-9ec8-98cd2879ae2d_terseLabel_en-US" xlink:label="lab_us-gaap_LeaseCostTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Components of operating lease expense</link:label>
    <link:label id="lab_us-gaap_LeaseCostTableTextBlock_label_en-US" xlink:label="lab_us-gaap_LeaseCostTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease, Cost [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCostTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseCostTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LeaseCostTableTextBlock" xlink:to="lab_us-gaap_LeaseCostTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CollateralBasedMeasurementsValuationTechniqueMember_0e87ab5d-9d2a-44da-98d5-95b575450168_terseLabel_en-US" xlink:label="lab_source_CollateralBasedMeasurementsValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral based measurements</link:label>
    <link:label id="lab_source_CollateralBasedMeasurementsValuationTechniqueMember_label_en-US" xlink:label="lab_source_CollateralBasedMeasurementsValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral Based Measurements Valuation Technique [Member]</link:label>
    <link:label id="lab_source_CollateralBasedMeasurementsValuationTechniqueMember_documentation_en-US" xlink:label="lab_source_CollateralBasedMeasurementsValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the collateral based measurements used to measure fair value.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CollateralBasedMeasurementsValuationTechniqueMember" xlink:href="source-20211231.xsd#source_CollateralBasedMeasurementsValuationTechniqueMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CollateralBasedMeasurementsValuationTechniqueMember" xlink:to="lab_source_CollateralBasedMeasurementsValuationTechniqueMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote_e99d73a3-3f2c-49e2-9fcc-590ad68931ef_terseLabel_en-US" xlink:label="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Federal Home Loan Bank borrowings, fixed rate notes</link:label>
    <link:label id="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote_label_en-US" xlink:label="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Federal Home Loan Bank Borrowing Fixed Rate Note</link:label>
    <link:label id="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote_documentation_en-US" xlink:label="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the number of fixed rate notes held of Federal Home Loan Bank Borrowings.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote" xlink:href="source-20211231.xsd#source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote" xlink:to="lab_source_NumberOfFederalHomeLoanBankBorrowingFixedRateNote" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_18e8f87b-8e5f-4275-8a0c-66e849fbcdbf_terseLabel_en-US" xlink:label="lab_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]</link:label>
    <link:label id="lab_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_label_en-US" xlink:label="lab_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:to="lab_us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfImpairedFinancingReceivableTable_4b4aa44c-a03f-422b-8acd-04f0e365624c_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of average recorded investment and interest income recognized on impaired loans and leases, segregated by class</link:label>
    <link:label id="lab_us-gaap_ScheduleOfImpairedFinancingReceivableTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Impaired Financing Receivable [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfImpairedFinancingReceivableTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:to="lab_us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DemandDepositAccounts_a18200f5-76be-43c7-b454-849d376ed64b_terseLabel_en-US" xlink:label="lab_us-gaap_DemandDepositAccounts" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest-bearing demand</link:label>
    <link:label id="lab_us-gaap_DemandDepositAccounts_label_en-US" xlink:label="lab_us-gaap_DemandDepositAccounts" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Demand Deposit Accounts</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DemandDepositAccounts" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DemandDepositAccounts"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DemandDepositAccounts" xlink:to="lab_us-gaap_DemandDepositAccounts" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ExpectedLifeOfUnderlyingCollateral_967761a2-23cc-42dc-9ab4-dd543a127175_terseLabel_en-US" xlink:label="lab_source_ExpectedLifeOfUnderlyingCollateral" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expected life of underlying collateral</link:label>
    <link:label id="lab_source_ExpectedLifeOfUnderlyingCollateral_label_en-US" xlink:label="lab_source_ExpectedLifeOfUnderlyingCollateral" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ExpectedLifeOfUnderlyingCollateral</link:label>
    <link:label id="lab_source_ExpectedLifeOfUnderlyingCollateral_documentation_en-US" xlink:label="lab_source_ExpectedLifeOfUnderlyingCollateral" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expected life of underlying collateral</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ExpectedLifeOfUnderlyingCollateral" xlink:href="source-20211231.xsd#source_ExpectedLifeOfUnderlyingCollateral"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ExpectedLifeOfUnderlyingCollateral" xlink:to="lab_source_ExpectedLifeOfUnderlyingCollateral" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeCollateralRightToReclaimCash_3939e0c9-648e-4487-b6cd-2dabcde5ce64_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeCollateralRightToReclaimCash" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash Collateral Pledged</link:label>
    <link:label id="lab_us-gaap_DerivativeCollateralRightToReclaimCash_label_en-US" xlink:label="lab_us-gaap_DerivativeCollateralRightToReclaimCash" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative, Collateral, Right to Reclaim Cash</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimCash" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeCollateralRightToReclaimCash"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeCollateralRightToReclaimCash" xlink:to="lab_us-gaap_DerivativeCollateralRightToReclaimCash" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases_cdf0326f-5b56-41e5-ac3e-9d991a09cdc4_terseLabel_en-US" xlink:label="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expense for payments of personal property taxes on operating leased equipment</link:label>
    <link:label id="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases_label_en-US" xlink:label="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expense Related to Personal Property Tax Payments on Operating Leases</link:label>
    <link:label id="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases_documentation_en-US" xlink:label="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Expense related to personal property tax payments on operating leased equipment.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases" xlink:href="source-20211231.xsd#source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases" xlink:to="lab_source_ExpenseRelatedtoPersonalPropertyTaxPaymentsonOperatingLeases" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InvestmentPolicyTextBlock_568d4da5-c44f-48b8-b1a7-9bd0ab561166_terseLabel_en-US" xlink:label="lab_us-gaap_InvestmentPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Securities</link:label>
    <link:label id="lab_us-gaap_InvestmentPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_InvestmentPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InvestmentPolicyTextBlock" xlink:to="lab_us-gaap_InvestmentPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInFinancingActivities_718035b5-7f2c-49fc-8d7a-224c95471acd_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in financing activities</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInFinancingActivities_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Cash Provided by (Used in) Financing Activities</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="lab_us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsOther_3823d634-e38a-44b4-bd93-093a3b0d3cf4_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsOther" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Tax Credit Carryforwards, Other</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsOther_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsOther" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Tax Credit Carryforwards, Other</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsOther" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsOther"/>
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    <link:label id="lab_us-gaap_TreasuryStockValue_22889578-ed32-40db-a7cb-487fba95c5c5_negatedLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockValue" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cost of common stock in treasury (3,466,162 shares at December&#160;31, 2021 and 2,816,557 shares at December&#160;31, 2020)</link:label>
    <link:label id="lab_us-gaap_TreasuryStockValue_label_en-US" xlink:label="lab_us-gaap_TreasuryStockValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock, Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TreasuryStockValue" xlink:to="lab_us-gaap_TreasuryStockValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_7c13a8b2-679a-4dd8-afa2-1db0bcba925a_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Vesting period</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeLossFromEquityMethodInvestments_bdbccf33-072b-4b69-b8cd-3a6c03cd3913_verboseLabel_en-US" xlink:label="lab_us-gaap_IncomeLossFromEquityMethodInvestments" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity in undistributed income of subsidiaries</link:label>
    <link:label id="lab_us-gaap_IncomeLossFromEquityMethodInvestments_ef94f0a5-b0cb-49b9-9a19-56a35ba4264e_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_IncomeLossFromEquityMethodInvestments" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity (undistributed) distributed in excess of income of subsidiaries</link:label>
    <link:label id="lab_us-gaap_IncomeLossFromEquityMethodInvestments_label_en-US" xlink:label="lab_us-gaap_IncomeLossFromEquityMethodInvestments" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income (Loss) from Equity Method Investments</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeLossFromEquityMethodInvestments" xlink:to="lab_us-gaap_IncomeLossFromEquityMethodInvestments" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueDisclosuresTextBlock_de689f47-ca82-40b5-a4df-4d927df9c9d3_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueDisclosuresTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Measurements</link:label>
    <link:label id="lab_us-gaap_FairValueDisclosuresTextBlock_label_en-US" xlink:label="lab_us-gaap_FairValueDisclosuresTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Disclosures [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueDisclosuresTextBlock" xlink:to="lab_us-gaap_FairValueDisclosuresTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1_cac166ab-16b6-44e4-b776-84a7eece8074_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring, Subsequent Default</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring, Subsequent Default</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:to="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_294885df-761d-4250-a895-af4a3eda28b3_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued interest receivable on loans and leases</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Accrued Interest, after Allowance for Credit Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss" xlink:to="lab_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss" xlink:type="arc" order="1"/>
    <link:label id="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases_29bd74e1-610f-4913-b3cf-c39cda6bad66_verboseLabel_en-US" xlink:label="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in equipment owned under operating leases</link:label>
    <link:label id="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases_label_en-US" xlink:label="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments for Proceeds from Equipment Owned under Operating Leases</link:label>
    <link:label id="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases_documentation_en-US" xlink:label="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents the net cash inflow (outflow) for the change in the beginning and end of period of equipment owned under contractual arrangements classified as operating leases.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases" xlink:href="source-20211231.xsd#source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases" xlink:to="lab_source_PaymentsForProceedsFromEquipmentOwnedUnderOperatingLeases" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueAmortization1_f5e0e058-e66d-440f-bb1d-cf87fab24258_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueAmortization1" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amortization</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueAmortization1_label_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueAmortization1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Cost, Amortization</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtAmortizedValueAmortization1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ServicingAssetAtAmortizedValueAmortization1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ServicingAssetAtAmortizedValueAmortization1" xlink:to="lab_us-gaap_ServicingAssetAtAmortizedValueAmortization1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy_474c73fb-4a48-4848-8572-57a5f3fd11ad_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy Amount</link:label>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy_label_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Tier One Leverage Capital, Capital Adequacy, Minimum</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:to="lab_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_19fd91ae-c765-46a7-b370-8a5a08183b06_terseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2024</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_label_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Asset, Expected Amortization, Year Three</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:to="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommonStockNoParValue_49cf6720-7bc7-4646-add7-664e6ad87e02_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockNoParValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Stock, Par or Stated Value Per Share</link:label>
    <link:label id="lab_us-gaap_CommonStockNoParValue_label_en-US" xlink:label="lab_us-gaap_CommonStockNoParValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Stock, No Par Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockNoParValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockNoParValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommonStockNoParValue" xlink:to="lab_us-gaap_CommonStockNoParValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable_0eda8f50-277c-4c0e-adad-72181194e773_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:to="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:type="arc" order="1"/>
    <link:label id="lab_source_FurnitureAndEquipmentExpense_d5f8db1f-b003-4e1a-9da3-581703417a0e_terseLabel_en-US" xlink:label="lab_source_FurnitureAndEquipmentExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Furniture and equipment</link:label>
    <link:label id="lab_source_FurnitureAndEquipmentExpense_label_en-US" xlink:label="lab_source_FurnitureAndEquipmentExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Furniture and Equipment Expense</link:label>
    <link:label id="lab_source_FurnitureAndEquipmentExpense_documentation_en-US" xlink:label="lab_source_FurnitureAndEquipmentExpense" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents equipment expense including depreciation, repairs, rentals, and service contract costs. This item also includes equipment purchases which do not qualify for capitalization in accordance with the entity's accounting policy. This item also includes furniture expenses, software maintenance, software license fees and computer processing costs such as website maintenance.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_FurnitureAndEquipmentExpense" xlink:href="source-20211231.xsd#source_FurnitureAndEquipmentExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_FurnitureAndEquipmentExpense" xlink:to="lab_source_FurnitureAndEquipmentExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableforsaleSecuritiesMember_b403fa99-df02-4b47-905b-7ec94ecfb6dd_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableforsaleSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment securities available-for-sale</link:label>
    <link:label id="lab_us-gaap_AvailableforsaleSecuritiesMember_label_en-US" xlink:label="lab_us-gaap_AvailableforsaleSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Available-for-sale Securities [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableforsaleSecuritiesMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableforsaleSecuritiesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableforsaleSecuritiesMember" xlink:to="lab_us-gaap_AvailableforsaleSecuritiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_BusinessCombinationsPolicy_719de7e1-aae9-4fc3-87dd-e8ec09b0b91f_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationsPolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combinations</link:label>
    <link:label id="lab_us-gaap_BusinessCombinationsPolicy_label_en-US" xlink:label="lab_us-gaap_BusinessCombinationsPolicy" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Combinations Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationsPolicy" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationsPolicy"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BusinessCombinationsPolicy" xlink:to="lab_us-gaap_BusinessCombinationsPolicy" xlink:type="arc" order="1"/>
    <link:label id="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember_6a611046-3177-4511-babc-ceecbda71458_terseLabel_en-US" xlink:label="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Discount for lack of marketability and current conditions</link:label>
    <link:label id="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember_label_en-US" xlink:label="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Input Discount For Lack of Marketability and Current Conditions [Member]</link:label>
    <link:label id="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember_documentation_en-US" xlink:label="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement input using amount by which value of business ownership interest is reduced to reflect lack of ability to convert business interest into cash quickly with the impact of current conditions.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember" xlink:href="source-20211231.xsd#source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember" xlink:to="lab_source_MeasurementInputDiscountForLackofMarketabilityandCurrentConditionsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested_f88b6f65-12fe-44c6-bc91-398e3dfe8022_terseLabel_en-US" xlink:label="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employee deferral that is always vested (as a percent)</link:label>
    <link:label id="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested_label_en-US" xlink:label="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Defined Contribution Plan, Employee Deferral Percentage, Vested</link:label>
    <link:label id="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested_documentation_en-US" xlink:label="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the percentage of the employee deferral that is always vested.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DefinedContributionPlanEmployeeDeferralPercentageVested" xlink:href="source-20211231.xsd#source_DefinedContributionPlanEmployeeDeferralPercentageVested"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DefinedContributionPlanEmployeeDeferralPercentageVested" xlink:to="lab_source_DefinedContributionPlanEmployeeDeferralPercentageVested" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SubordinatedBorrowingLineItems_a87f94b7-75de-43b5-8155-e6e574894bab_terseLabel_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated notes</link:label>
    <link:label id="lab_us-gaap_SubordinatedBorrowingLineItems_label_en-US" xlink:label="lab_us-gaap_SubordinatedBorrowingLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated Borrowing [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedBorrowingLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubordinatedBorrowingLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SubordinatedBorrowingLineItems" xlink:to="lab_us-gaap_SubordinatedBorrowingLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd_6ecdb721-8c71-41e9-bf12-2508de2a81dd_terseLabel_en-US" xlink:label="lab_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest rate on Federal Home Loan Bank borrowings (as a percent)</link:label>
    <link:label id="lab_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd_label_en-US" xlink:label="lab_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:to="lab_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestAndDividendIncomeOperatingAbstract_469e6021-fd72-403d-983d-cca838e59166_terseLabel_en-US" xlink:label="lab_us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest income:</link:label>
    <link:label id="lab_us-gaap_InterestAndDividendIncomeOperatingAbstract_label_en-US" xlink:label="lab_us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest and Dividend Income, Operating [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestAndDividendIncomeOperatingAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:to="lab_us-gaap_InterestAndDividendIncomeOperatingAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans_1fb2c335-63b8-47c7-94c8-ed4bceea288c_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of executive stock award plans</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans_label_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share Based Compensation Arrangement by Share Based Payment Award, Number of Executive Stock Award Plans</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans_documentation_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the number of active executive stock award plans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans" xlink:href="source-20211231.xsd#source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans" xlink:to="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfExecutiveStockAwardPlans" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_DocumentPeriodEndDate_11340e9b-d03b-4705-8a9d-730a117069a4_terseLabel_en-US" xlink:label="lab_dei_DocumentPeriodEndDate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Period End Date</link:label>
    <link:label id="lab_dei_DocumentPeriodEndDate_label_en-US" xlink:label="lab_dei_DocumentPeriodEndDate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Document Period End Date</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_DocumentPeriodEndDate"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_DocumentPeriodEndDate" xlink:to="lab_dei_DocumentPeriodEndDate" xlink:type="arc" order="1"/>
    <link:label id="lab_source_PaymentsForProceedsFromOtherInvestments_12aef09d-7006-4030-9258-caabe7f79b1c_verboseLabel_en-US" xlink:label="lab_source_PaymentsForProceedsFromOtherInvestments" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in other investments</link:label>
    <link:label id="lab_source_PaymentsForProceedsFromOtherInvestments_label_en-US" xlink:label="lab_source_PaymentsForProceedsFromOtherInvestments" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments for (Proceeds from) Other Investments</link:label>
    <link:label id="lab_source_PaymentsForProceedsFromOtherInvestments_documentation_en-US" xlink:label="lab_source_PaymentsForProceedsFromOtherInvestments" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element includes the following: (1) The net cash inflow (outflow) in Interest-bearing Deposits by banks in other financial institutions for periods of time exceeding 3 months including, for example, certificates of deposits. (2) The net cash outflow or inflow of Federal Home Loan Bank Stock during the period. Federal Home Loan Bank (or Federal Reserve Bank) stock is an equity interest in a Federal Home Loan Bank (or Federal Reserve Bank).</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_PaymentsForProceedsFromOtherInvestments" xlink:href="source-20211231.xsd#source_PaymentsForProceedsFromOtherInvestments"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_PaymentsForProceedsFromOtherInvestments" xlink:to="lab_source_PaymentsForProceedsFromOtherInvestments" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OffBalanceSheetCreditLossLiability_7c70e79c-75e2-4c29-b253-33661b763914_periodStartLabel_en-US" xlink:label="lab_us-gaap_OffBalanceSheetCreditLossLiability" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance, beginning of year</link:label>
    <link:label id="lab_us-gaap_OffBalanceSheetCreditLossLiability_c4f31d3b-b73e-4097-b2ee-7e4f4d900a48_periodEndLabel_en-US" xlink:label="lab_us-gaap_OffBalanceSheetCreditLossLiability" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance, end of year</link:label>
    <link:label id="lab_us-gaap_OffBalanceSheetCreditLossLiability_label_en-US" xlink:label="lab_us-gaap_OffBalanceSheetCreditLossLiability" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Off-Balance Sheet, Credit Loss, Liability</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffBalanceSheetCreditLossLiability" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OffBalanceSheetCreditLossLiability"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OffBalanceSheetCreditLossLiability" xlink:to="lab_us-gaap_OffBalanceSheetCreditLossLiability" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_ConsolidatedEntitiesDomain_86d5e242-9898-4ade-969e-378bb1f8607f_terseLabel_en-US" xlink:label="lab_srt_ConsolidatedEntitiesDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Consolidated Entities [Domain]</link:label>
    <link:label id="lab_srt_ConsolidatedEntitiesDomain_label_en-US" xlink:label="lab_srt_ConsolidatedEntitiesDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Consolidated Entities [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_ConsolidatedEntitiesDomain" xlink:to="lab_srt_ConsolidatedEntitiesDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit_cc4e8b2e-c750-42cd-aa62-03515631f027_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">State</link:label>
    <link:label id="lab_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit_label_en-US" xlink:label="lab_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred State and Local Income Tax Expense (Benefit)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:to="lab_us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_359b6e8a-5777-4119-b935-5afb0f112a36_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investing activities:</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:to="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentTextBlock_d0d33576-953c-45a0-b697-f83437415301_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of premises and equipment</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentTextBlock_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage_35d547ed-4be8-4c0e-a05e-6ff87c1f8af1_terseLabel_en-US" xlink:label="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employee's eligible compensation on which employer pays fixed contribution (as a percent)</link:label>
    <link:label id="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage_label_en-US" xlink:label="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Defined Contribution Plan, Employer Discretionary Contribution Percentage</link:label>
    <link:label id="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage_documentation_en-US" xlink:label="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the fixed percentage of eligible earnings that can be contributed by the employer.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage" xlink:href="source-20211231.xsd#source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage" xlink:to="lab_source_DefinedContributionPlanEmployerDiscretionaryContributionPercentage" xlink:type="arc" order="1"/>
    <link:label id="lab_source_NetInvestmentinOperatingLeaseFinancing_8dd1605d-d53f-4a5e-8147-1f3a9135c307_terseLabel_en-US" xlink:label="lab_source_NetInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equipment owned under operating leases, net</link:label>
    <link:label id="lab_source_NetInvestmentinOperatingLeaseFinancing_2830960b-3d3c-421e-a597-107d061ca403_totalLabel_en-US" xlink:label="lab_source_NetInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net investment in operating lease financings</link:label>
    <link:label id="lab_source_NetInvestmentinOperatingLeaseFinancing_label_en-US" xlink:label="lab_source_NetInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Investment in Operating Lease Financing</link:label>
    <link:label id="lab_source_NetInvestmentinOperatingLeaseFinancing_documentation_en-US" xlink:label="lab_source_NetInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The amount of property, by major property class, net of accumulated depreciation, subject to or available for lease as of the balance sheet date.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_NetInvestmentinOperatingLeaseFinancing" xlink:href="source-20211231.xsd#source_NetInvestmentinOperatingLeaseFinancing"/>
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    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearFour_4467a34b-943e-4e88-ac93-9ec0171cc1dd_terseLabel_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearFour" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2025</link:label>
    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearFour_label_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearFour" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Time Deposit Maturities, Year Four</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDepositMaturitiesYearFour" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TimeDepositMaturitiesYearFour"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TimeDepositMaturitiesYearFour" xlink:to="lab_us-gaap_TimeDepositMaturitiesYearFour" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeStatementLocationDomain_b485ea37-5fbd-414b-99f8-0beec6ba9eab_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeStatementLocationDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Statement Location [Domain]</link:label>
    <link:label id="lab_us-gaap_IncomeStatementLocationDomain_label_en-US" xlink:label="lab_us-gaap_IncomeStatementLocationDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Statement Location [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeStatementLocationDomain" xlink:to="lab_us-gaap_IncomeStatementLocationDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_source_NonBankingSubsidiaryMember_ec57e5de-9291-446e-a9f7-002085957143_terseLabel_en-US" xlink:label="lab_source_NonBankingSubsidiaryMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Non-bank subsidiaries</link:label>
    <link:label id="lab_source_NonBankingSubsidiaryMember_label_en-US" xlink:label="lab_source_NonBankingSubsidiaryMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Non Banking Subsidiary [Member]</link:label>
    <link:label id="lab_source_NonBankingSubsidiaryMember_documentation_en-US" xlink:label="lab_source_NonBankingSubsidiaryMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to subsidiary which is not engaged in banking business.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_NonBankingSubsidiaryMember" xlink:href="source-20211231.xsd#source_NonBankingSubsidiaryMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_NonBankingSubsidiaryMember" xlink:to="lab_source_NonBankingSubsidiaryMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_2de1e4d1-48d9-4c13-b781-5d3c854d4843_terseLabel_en-US" xlink:label="lab_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Non-cash transactions:</link:label>
    <link:label id="lab_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_label_en-US" xlink:label="lab_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="lab_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_CondensedFinancialStatementsCaptionsLineItems_57b09e4d-3f82-42c0-aefe-efae638287ac_terseLabel_en-US" xlink:label="lab_srt_CondensedFinancialStatementsCaptionsLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">1st Source Corporation (Parent Company Only) Financial Information</link:label>
    <link:label id="lab_srt_CondensedFinancialStatementsCaptionsLineItems_label_en-US" xlink:label="lab_srt_CondensedFinancialStatementsCaptionsLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Condensed Financial Statements, Captions [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems" xlink:to="lab_srt_CondensedFinancialStatementsCaptionsLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestReceivable_e9fa7d15-afa0-4a87-8a32-a9ccf5266615_terseLabel_en-US" xlink:label="lab_us-gaap_InterestReceivable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest receivable</link:label>
    <link:label id="lab_us-gaap_InterestReceivable_label_en-US" xlink:label="lab_us-gaap_InterestReceivable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Receivable</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestReceivable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestReceivable" xlink:to="lab_us-gaap_InterestReceivable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentNet_48146f46-8e88-4198-b751-10bb9d87c4f8_totalLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentNet" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net premises and equipment</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentNet_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment, Net</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingExpenses_91966ddb-41c5-4ac5-9473-62794b4dec85_totalLabel_en-US" xlink:label="lab_us-gaap_OperatingExpenses" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total expenses</link:label>
    <link:label id="lab_us-gaap_OperatingExpenses_label_en-US" xlink:label="lab_us-gaap_OperatingExpenses" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Expenses</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingExpenses"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingExpenses" xlink:to="lab_us-gaap_OperatingExpenses" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_2a4c90a7-8ca0-4dc3-bba5-c8ecf9fc1f9b_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing receivable originated during current fiscal year</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Year One, Originated, Current Fiscal Year</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear" xlink:to="lab_us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure_26480068-c7e8-462d-a18d-1381df61713b_terseLabel_en-US" xlink:label="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgages held for sale</link:label>
    <link:label id="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure_93b1ee51-ebc5-4d9d-b44a-b3a73c4d2f9d_verboseLabel_en-US" xlink:label="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair value carrying amount</link:label>
    <link:label id="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure_label_en-US" xlink:label="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgages Held-for-sale, Fair Value Disclosure</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgagesHeldForSaleFairValueDisclosure"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:to="lab_us-gaap_MortgagesHeldForSaleFairValueDisclosure" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_53cd3043-ddab-4b1a-9428-5f614f388c10_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total gains or losses (realized/unrealized): included in other comprehensive income</link:label>
    <link:label id="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss_label_en-US" xlink:label="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:to="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber_78eb7407-120c-44e7-bd26-f8fbd3d06c2e_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of stock-based employee compensation plans</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber_label_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share Based Compensation Arrangement by Share Based Payment Award, Plan Number</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber_documentation_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the number of active stock-based employee compensation plans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber" xlink:href="source-20211231.xsd#source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber" xlink:to="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanNumber" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RepaymentsOfLongTermDebt_49a413ce-ac4d-4110-9636-b92a5a057787_negatedLabel_en-US" xlink:label="lab_us-gaap_RepaymentsOfLongTermDebt" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments on long-term debt</link:label>
    <link:label id="lab_us-gaap_RepaymentsOfLongTermDebt_e442dd51-bcc2-4217-adec-4ac1e42b6f36_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_RepaymentsOfLongTermDebt" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments on long-term debt and mandatorily redeemable securities</link:label>
    <link:label id="lab_us-gaap_RepaymentsOfLongTermDebt_label_en-US" xlink:label="lab_us-gaap_RepaymentsOfLongTermDebt" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repayments of Long-term Debt</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RepaymentsOfLongTermDebt" xlink:to="lab_us-gaap_RepaymentsOfLongTermDebt" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EarningsPerShareAbstract_839526e2-054c-4031-b038-52645d19a237_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Earnings Per Share [Abstract]</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareAbstract_label_en-US" xlink:label="lab_us-gaap_EarningsPerShareAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Earnings Per Share [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareAbstract"/>
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    <link:label id="lab_source_ScheduleOfMaturitiesOfTimeDepositsCurrentTableTextBlock_8f3f769d-3104-495e-8765-4525daecb2c1_terseLabel_en-US" xlink:label="lab_source_ScheduleOfMaturitiesOfTimeDepositsCurrentTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of certificates of deposit of $250,000 or more and other time deposits of $250,000 or more by time remaining until maturity</link:label>
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    <link:label id="lab_us-gaap_InterestBearingDepositLiabilities_40a67bc6-605f-469e-8604-74bf20c1132e_totalLabel_en-US" xlink:label="lab_us-gaap_InterestBearingDepositLiabilities" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total interest-bearing deposits</link:label>
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    <link:label id="lab_source_NetGainOnSaleOfOtherRealEstateAndRepossessions_86ec9e42-5ddb-4548-87fd-335f8deb613f_negatedTerseLabel_en-US" xlink:label="lab_source_NetGainOnSaleOfOtherRealEstateAndRepossessions" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net gains on sale of other real estate and repossessions</link:label>
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    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_1295f968-f92c-4606-a574-eea78f462e30_terseLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of available-for-sale debt securities in an unrealized loss position</link:label>
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    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperations_2018d137-a75d-4fe6-990f-ce02885c1d5f_totalLabel_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total income tax expense (benefit) (as a percent)</link:label>
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    <link:label id="lab_us-gaap_NoninterestIncomeOtherOperatingIncome_8ec37204-d28e-492b-b819-40f54dc57293_terseLabel_en-US" xlink:label="lab_us-gaap_NoninterestIncomeOtherOperatingIncome" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
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    <link:label id="lab_us-gaap_ServicingAssetMeasurementInput_f4fd8059-3c56-41b9-8170-d9b9f8712aa8_verboseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage servicing rights unobservable inputs (as a percent)</link:label>
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    <link:label id="lab_source_AuctionValuesValuationTechniqueMember_1bd5395b-3994-4773-abab-aab135b7ab43_terseLabel_en-US" xlink:label="lab_source_AuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auction values</link:label>
    <link:label id="lab_source_AuctionValuesValuationTechniqueMember_label_en-US" xlink:label="lab_source_AuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auction Values Valuation Technique [Member]</link:label>
    <link:label id="lab_source_AuctionValuesValuationTechniqueMember_documentation_en-US" xlink:label="lab_source_AuctionValuesValuationTechniqueMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the auction values valuation technique used to measure fair value.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_AuctionValuesValuationTechniqueMember" xlink:href="source-20211231.xsd#source_AuctionValuesValuationTechniqueMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_AuctionValuesValuationTechniqueMember" xlink:to="lab_source_AuctionValuesValuationTechniqueMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_BusinessDevelopmentAndMarketingExpense_13dfd153-ad1e-416e-a68f-57ce92fb71e1_terseLabel_en-US" xlink:label="lab_source_BusinessDevelopmentAndMarketingExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business development and marketing</link:label>
    <link:label id="lab_source_BusinessDevelopmentAndMarketingExpense_label_en-US" xlink:label="lab_source_BusinessDevelopmentAndMarketingExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Business Development and Marketing Expense</link:label>
    <link:label id="lab_source_BusinessDevelopmentAndMarketingExpense_documentation_en-US" xlink:label="lab_source_BusinessDevelopmentAndMarketingExpense" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element includes business development expense which involves the development of products and services, their delivery, design and their implementation. Business development includes a number of techniques designed to grow an economic enterprise. Such techniques include, but are not limited to, assessments of marketing opportunities and target markets, intelligence gathering on customers and competitors, generating leads for possible sales, follow-up sales activity, formal proposal writing and business model design. Business development involves evaluating a business and then realizing its full potential, using such tools as marketing, sales, information management and customer service. Also includes the total expense recognized in the period for promotion, public relations, and brand or product advertising.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_BusinessDevelopmentAndMarketingExpense" xlink:href="source-20211231.xsd#source_BusinessDevelopmentAndMarketingExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_BusinessDevelopmentAndMarketingExpense" xlink:to="lab_source_BusinessDevelopmentAndMarketingExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MeasurementInputDiscountRateMember_06bd21c2-0b8b-49bc-bb4e-e45e90f7501a_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputDiscountRateMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Discount rate</link:label>
    <link:label id="lab_us-gaap_MeasurementInputDiscountRateMember_label_en-US" xlink:label="lab_us-gaap_MeasurementInputDiscountRateMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Input, Discount Rate [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MeasurementInputDiscountRateMember" xlink:to="lab_us-gaap_MeasurementInputDiscountRateMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears_98429560-d308-48fe-b621-c43cb806b2cb_terseLabel_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2026</link:label>
    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears_label_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears" xlink:to="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFiveYears" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearOne_447672cc-a5e2-4e13-805e-adb2b24e093e_terseLabel_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearOne" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2022</link:label>
    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearOne_label_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearOne" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Time Deposit Maturities, Year One</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDepositMaturitiesYearOne" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TimeDepositMaturitiesYearOne"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TimeDepositMaturitiesYearOne" xlink:to="lab_us-gaap_TimeDepositMaturitiesYearOne" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LeasesAbstract_9143c4e5-a440-4ed2-87fd-39baa9cf4e33_terseLabel_en-US" xlink:label="lab_us-gaap_LeasesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Leases [Abstract]</link:label>
    <link:label id="lab_us-gaap_LeasesAbstract_label_en-US" xlink:label="lab_us-gaap_LeasesAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Leases [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeasesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeasesAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LeasesAbstract" xlink:to="lab_us-gaap_LeasesAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CapitalRequiredToBeWellCapitalized_6b7a5042-a51d-461a-a622-79144d2a8f0f_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalRequiredToBeWellCapitalized" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">To Be Well Capitalized Under Prompt Corrective Action Provisions Amount</link:label>
    <link:label id="lab_us-gaap_CapitalRequiredToBeWellCapitalized_label_en-US" xlink:label="lab_us-gaap_CapitalRequiredToBeWellCapitalized" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Total Risk-Based Capital, Well Capitalized, Minimum</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalRequiredToBeWellCapitalized" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalRequiredToBeWellCapitalized"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CapitalRequiredToBeWellCapitalized" xlink:to="lab_us-gaap_CapitalRequiredToBeWellCapitalized" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxPolicyTextBlock_24159983-0131-42e7-8062-0225cf9d3763_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Taxes</link:label>
    <link:label id="lab_us-gaap_IncomeTaxPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_IncomeTaxPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Tax, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeTaxPolicyTextBlock" xlink:to="lab_us-gaap_IncomeTaxPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_fe802492-73fc-46e6-bb2c-82e5665763e9_terseLabel_en-US" xlink:label="lab_us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">London Interbank Offered Rate (LIBOR)</link:label>
    <link:label id="lab_us-gaap_LondonInterbankOfferedRateLIBORMember_label_en-US" xlink:label="lab_us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">London Interbank Offered Rate (LIBOR) [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:to="lab_us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsLineItems_3fc07fc1-dd79-4028-bc57-f8747a0e0717_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and leases classified as TDR</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsLineItems_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableModificationsLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableModificationsLineItems" xlink:to="lab_us-gaap_FinancingReceivableModificationsLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement_8dc549d7-0ff2-40dd-a5c0-b2002f8e1adb_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Amounts of Recognized Liabilities</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement_label_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement" xlink:to="lab_us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NoninterestExpense_bbd33991-15ef-4438-9d95-d4cf348915f2_totalLabel_en-US" xlink:label="lab_us-gaap_NoninterestExpense" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total noninterest expense</link:label>
    <link:label id="lab_us-gaap_NoninterestExpense_label_en-US" xlink:label="lab_us-gaap_NoninterestExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noninterest Expense</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpense" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoninterestExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NoninterestExpense" xlink:to="lab_us-gaap_NoninterestExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityAddressPostalZipCode_c9858949-12e9-4df1-a358-853152591276_terseLabel_en-US" xlink:label="lab_dei_EntityAddressPostalZipCode" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Postal Zip Code</link:label>
    <link:label id="lab_dei_EntityAddressPostalZipCode_label_en-US" xlink:label="lab_dei_EntityAddressPostalZipCode" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Postal Zip Code</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressPostalZipCode"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityAddressPostalZipCode" xlink:to="lab_dei_EntityAddressPostalZipCode" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestExpenseOther_6c3caed7-4701-428d-965a-094a8585da3e_terseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseOther" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest expense</link:label>
    <link:label id="lab_us-gaap_InterestExpenseOther_label_en-US" xlink:label="lab_us-gaap_InterestExpenseOther" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Expense, Other</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOther" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseOther"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestExpenseOther" xlink:to="lab_us-gaap_InterestExpenseOther" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_a945868a-290f-443f-addc-3e15677f86b8_totalLabel_en-US" xlink:label="lab_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Weighted average shares outstanding for diluted earnings per common share</link:label>
    <link:label id="lab_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_label_en-US" xlink:label="lab_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Weighted Average Number of Shares Outstanding, Diluted</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="lab_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree_d0eeb3e7-7136-44ab-a746-cc697e9947f5_terseLabel_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2024</link:label>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree_label_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Value Expected Amortization in Year Three</link:label>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree_documentation_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the amount of expense to be charged against earnings in the year three following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree" xlink:href="source-20211231.xsd#source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree" xlink:to="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearThree" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxDisclosureTextBlock_2575814c-38f0-43e0-942e-2a8b4b848a23_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Taxes</link:label>
    <link:label id="lab_us-gaap_IncomeTaxDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_IncomeTaxDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Tax Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeTaxDisclosureTextBlock" xlink:to="lab_us-gaap_IncomeTaxDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RelatedPartyDomain_84cb8e57-d67b-41c3-bb66-77cda516e491_terseLabel_en-US" xlink:label="lab_us-gaap_RelatedPartyDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Related Party [Domain]</link:label>
    <link:label id="lab_us-gaap_RelatedPartyDomain_label_en-US" xlink:label="lab_us-gaap_RelatedPartyDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Related Party [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RelatedPartyDomain" xlink:to="lab_us-gaap_RelatedPartyDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_source_SolarLoansMember_2b42b4ff-10f7-44b2-a46c-16376f2d52ae_terseLabel_en-US" xlink:label="lab_source_SolarLoansMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Solar</link:label>
    <link:label id="lab_source_SolarLoansMember_label_en-US" xlink:label="lab_source_SolarLoansMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Solar Loans [Member]</link:label>
    <link:label id="lab_source_SolarLoansMember_documentation_en-US" xlink:label="lab_source_SolarLoansMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Portfolio segment of financial receivables related to solar loans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_SolarLoansMember" xlink:href="source-20211231.xsd#source_SolarLoansMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_SolarLoansMember" xlink:to="lab_source_SolarLoansMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_211f5c4a-2eea-4125-bb10-6e754a47054f_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Basis Spread on Variable Rate (as a percent)</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument, Basis Spread on Variable Rate</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:to="lab_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis_b7e8bebf-1221-45fd-86b9-2d2ef4ee94b0_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Due in one year or less</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableDeferredIncome_da9da642-a65e-4681-ae06-afade424c962_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableDeferredIncome" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred loan and lease costs</link:label>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableDeferredIncome_label_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableDeferredIncome" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases Receivable, Deferred Income</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableDeferredIncome" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableDeferredIncome"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LoansAndLeasesReceivableDeferredIncome" xlink:to="lab_us-gaap_LoansAndLeasesReceivableDeferredIncome" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StatementOfCashFlowsAbstract_48b82d77-7f6e-411f-a96d-bfae63e7012c_terseLabel_en-US" xlink:label="lab_us-gaap_StatementOfCashFlowsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
    <link:label id="lab_us-gaap_StatementOfCashFlowsAbstract_label_en-US" xlink:label="lab_us-gaap_StatementOfCashFlowsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfCashFlowsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementOfCashFlowsAbstract" xlink:to="lab_us-gaap_StatementOfCashFlowsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_16223589-d8ea-410f-983f-916c241430d4_terseLabel_en-US" xlink:label="lab_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unconsolidated maximum exposure to loss</link:label>
    <link:label id="lab_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount_label_en-US" xlink:label="lab_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount" xlink:to="lab_us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OccupancyNet_6085a0f1-f762-4223-ac6d-8a30b7f7aeb2_terseLabel_en-US" xlink:label="lab_us-gaap_OccupancyNet" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net occupancy</link:label>
    <link:label id="lab_us-gaap_OccupancyNet_1518e7fc-a53d-4c1d-9830-c75595da9f5f_verboseLabel_en-US" xlink:label="lab_us-gaap_OccupancyNet" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Occupancy</link:label>
    <link:label id="lab_us-gaap_OccupancyNet_label_en-US" xlink:label="lab_us-gaap_OccupancyNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Occupancy, Net</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OccupancyNet" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OccupancyNet"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OccupancyNet" xlink:to="lab_us-gaap_OccupancyNet" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NondesignatedMember_ef2ab75f-d921-4be5-8d35-f34a7e3f7c32_terseLabel_en-US" xlink:label="lab_us-gaap_NondesignatedMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Non-hedging derivative financial instruments</link:label>
    <link:label id="lab_us-gaap_NondesignatedMember_label_en-US" xlink:label="lab_us-gaap_NondesignatedMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Not Designated as Hedging Instrument [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NondesignatedMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NondesignatedMember" xlink:to="lab_us-gaap_NondesignatedMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c92a9ad1-aa4a-4aa7-ac6d-64befe101d21_terseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Assets, Major Class Name [Domain]</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_label_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Assets, Major Class Name [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="lab_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityAddressAddressLine1_bd518dcb-7af9-4e09-bbb4-7f23b8f50bf8_terseLabel_en-US" xlink:label="lab_dei_EntityAddressAddressLine1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Address Line One</link:label>
    <link:label id="lab_dei_EntityAddressAddressLine1_label_en-US" xlink:label="lab_dei_EntityAddressAddressLine1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, Address Line One</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressAddressLine1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityAddressAddressLine1" xlink:to="lab_dei_EntityAddressAddressLine1" xlink:type="arc" order="1"/>
    <link:label id="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced_81711c73-89f0-4fc7-a543-03a62ffd147b_terseLabel_en-US" xlink:label="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of significant lessee leases that have not yet commenced</link:label>
    <link:label id="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced_label_en-US" xlink:label="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of significant lessee leases that have not yet commenced</link:label>
    <link:label id="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced_documentation_en-US" xlink:label="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of significant lessee leases that have not yet commenced as of the end of the reporting period.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_Numberofsignificantlesseeleasesthathavenotyetcommenced" xlink:href="source-20211231.xsd#source_Numberofsignificantlesseeleasesthathavenotyetcommenced"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_Numberofsignificantlesseeleasesthathavenotyetcommenced" xlink:to="lab_source_Numberofsignificantlesseeleasesthathavenotyetcommenced" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_7148f1f9-4bc4-48d9-a4fc-77c078c19438_negatedLabel_en-US" xlink:label="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated depreciation and amortization</link:label>
    <link:label id="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_label_en-US" xlink:label="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:to="lab_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember_3bad1df0-9a76-4f94-b101-eed130779ff2_terseLabel_en-US" xlink:label="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign government and other securities</link:label>
    <link:label id="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember_label_en-US" xlink:label="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Foreign Government and Other Debt Securities [Member]</link:label>
    <link:label id="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember_documentation_en-US" xlink:label="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the debt securities issued by a national, local or municipal government including any other debt securities not within the country of domicile of the reporting entity.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ForeignGovernmentAndOtherDebtSecuritiesMember" xlink:href="source-20211231.xsd#source_ForeignGovernmentAndOtherDebtSecuritiesMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ForeignGovernmentAndOtherDebtSecuritiesMember" xlink:to="lab_source_ForeignGovernmentAndOtherDebtSecuritiesMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts_a3011714-57aa-4d4e-a09a-02efb40433e5_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Allowance for credit losses</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Allowance for Credit Losses, Policy for Uncollectible Amounts [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts" xlink:to="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesPolicyForUncollectibleAmounts" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MeasurementInputCreditSpreadMember_692eedf1-304d-4ba2-bdc8-19da49e43a79_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputCreditSpreadMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Credit spread assumption</link:label>
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    <link:label id="lab_source_AllowanceForCreditLossesOnUnfundedLoanCommitmentsTableTextBlackTableTextBlock_8e56cb0e-ee2d-41b2-8499-84abf91b24d4_terseLabel_en-US" xlink:label="lab_source_AllowanceForCreditLossesOnUnfundedLoanCommitmentsTableTextBlackTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of changes in allowance for credit losses on unfunded loan commitments</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock_b097d6a1-1b11-4f52-ba76-770b0db3d5f4_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of actual and required capital amounts and ratios</link:label>
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    <link:label id="lab_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment_336414df-7a9e-4362-9557-24f0972e9723_terseLabel_en-US" xlink:label="lab_us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Average Recorded Investment</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_6079dca5-83f0-4a03-879a-ae7efc92c644_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in operating activities</link:label>
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    <link:label id="lab_us-gaap_DerivativeCollateralObligationToReturnSecurities_638c4d64-5465-4d3d-a210-0d06dca9a92e_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeCollateralObligationToReturnSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial instruments</link:label>
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    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearFive_b963ae74-da8b-4a1a-a2a0-09669bf7a309_terseLabel_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2026</link:label>
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    <link:label id="lab_source_AircraftMember_10868101-5040-4f7d-b74c-356abd814867_terseLabel_en-US" xlink:label="lab_source_AircraftMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Aircraft</link:label>
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    <link:label id="lab_source_AircraftMember_documentation_en-US" xlink:label="lab_source_AircraftMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Portfolio segment of financing receivables related to aircraft loans.</link:label>
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    <link:label id="lab_source_DefinedBenefitAndContributionPlanDisclosureLineItems_documentation_en-US" xlink:label="lab_source_DefinedBenefitAndContributionPlanDisclosureLineItems" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems_c9f36036-7435-429c-8ab7-ba61723ef133_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment [Line Items]</link:label>
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    <link:label id="lab_us-gaap_AutomobilesMember_996c9e7b-22d4-43af-a23c-8a9ee89ac0d2_terseLabel_en-US" xlink:label="lab_us-gaap_AutomobilesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Autos</link:label>
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    <link:label id="lab_us-gaap_DeferredIncomeTaxExpenseBenefit_5c4e6738-7842-4d38-99f0-86bba10d5a63_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred income taxes</link:label>
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    <link:label id="lab_source_FinancingReceivableNonTroubledDebtRestructuringModificationsAmount_656b97ad-cf8b-4310-b874-9f434fd10d4b_terseLabel_en-US" xlink:label="lab_source_FinancingReceivableNonTroubledDebtRestructuringModificationsAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">COVID-19 related loan and lease modifications</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostBasisRollingMaturityAbstract_54cc8d34-8da9-4949-befd-8c28283063f7_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostBasisRollingMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual maturities of investments in debt securities available-for-sale, Amortized Cost</link:label>
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    <link:label id="lab_us-gaap_InterestExpenseDeposits_18a053ec-ee8e-46ea-bf54-a6b981a6496f_terseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseDeposits" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deposits</link:label>
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    <link:label id="lab_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_ba7a5175-7834-44b6-bbe3-51f1b68a4c39_terseLabel_en-US" xlink:label="lab_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Assets:</link:label>
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    <link:label id="lab_source_OtherRealEstateMember_32d43fd2-7b64-4e69-acee-d9d2d1104244_terseLabel_en-US" xlink:label="lab_source_OtherRealEstateMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other real estate</link:label>
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    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_94825cc6-4038-42d1-bde5-72cc2df4a2b7_terseLabel_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statutory federal income tax (as a percent)</link:label>
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    <link:label id="lab_us-gaap_EarningsPerSharePolicyTextBlock_b7f8008b-15dc-48ef-875f-b533fa8e46f4_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerSharePolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Income Per Common Share</link:label>
    <link:label id="lab_us-gaap_EarningsPerSharePolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_EarningsPerSharePolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Earnings Per Share, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerSharePolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerSharePolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EarningsPerSharePolicyTextBlock" xlink:to="lab_us-gaap_EarningsPerSharePolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetIncomeLoss_6eb4352d-0a30-457a-9d73-538b7c91cee9_terseLabel_en-US" xlink:label="lab_us-gaap_NetIncomeLoss" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net income</link:label>
    <link:label id="lab_us-gaap_NetIncomeLoss_label_en-US" xlink:label="lab_us-gaap_NetIncomeLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Income (Loss) Attributable to Parent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetIncomeLoss" xlink:to="lab_us-gaap_NetIncomeLoss" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_421c3ae6-9b4c-4639-8eda-915e0b78dddc_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Hierarchy and NAV [Domain]</link:label>
    <link:label id="lab_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_label_en-US" xlink:label="lab_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Hierarchy and NAV [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="lab_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets_9baa54b1-74f3-4677-b59d-8c1a8be68acb_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)</link:label>
    <link:label id="lab_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets_label_en-US" xlink:label="lab_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Tier One Risk-Based Capital Ratio, Well Capitalized, Minimum</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets"/>
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    <link:label id="lab_us-gaap_OperatingLeaseRightOfUseAsset_efa1ed01-2983-47b4-8deb-eb3247b22611_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeaseRightOfUseAsset" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating lease right of use assets</link:label>
    <link:label id="lab_us-gaap_OperatingLeaseRightOfUseAsset_label_en-US" xlink:label="lab_us-gaap_OperatingLeaseRightOfUseAsset" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Right-of-Use Asset</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeaseRightOfUseAsset" xlink:to="lab_us-gaap_OperatingLeaseRightOfUseAsset" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NoninterestBearingDepositLiabilities_65138f52-bc3f-4be5-92f0-6de1a7f010e9_terseLabel_en-US" xlink:label="lab_us-gaap_NoninterestBearingDepositLiabilities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noninterest-bearing demand</link:label>
    <link:label id="lab_us-gaap_NoninterestBearingDepositLiabilities_label_en-US" xlink:label="lab_us-gaap_NoninterestBearingDepositLiabilities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noninterest-bearing Deposit Liabilities</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestBearingDepositLiabilities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoninterestBearingDepositLiabilities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NoninterestBearingDepositLiabilities" xlink:to="lab_us-gaap_NoninterestBearingDepositLiabilities" xlink:type="arc" order="1"/>
    <link:label id="lab_source_PPPLoanBalance_72105650-4d95-4e82-a49a-e06edfedb413_terseLabel_en-US" xlink:label="lab_source_PPPLoanBalance" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPP loan balance</link:label>
    <link:label id="lab_source_PPPLoanBalance_label_en-US" xlink:label="lab_source_PPPLoanBalance" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPPLoanBalance</link:label>
    <link:label id="lab_source_PPPLoanBalance_documentation_en-US" xlink:label="lab_source_PPPLoanBalance" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPP loan balance</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_PPPLoanBalance" xlink:href="source-20211231.xsd#source_PPPLoanBalance"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_PPPLoanBalance" xlink:to="lab_source_PPPLoanBalance" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeStatementLocationAxis_fc215ae4-931f-4dfc-8156-c82f0428e748_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeStatementLocationAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Statement Location [Axis]</link:label>
    <link:label id="lab_us-gaap_IncomeStatementLocationAxis_label_en-US" xlink:label="lab_us-gaap_IncomeStatementLocationAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Statement Location [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeStatementLocationAxis" xlink:to="lab_us-gaap_IncomeStatementLocationAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock_790ec80c-5510-457f-9f87-6a2b2b2f24c5_terseLabel_en-US" xlink:label="lab_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">1st Source Corporation (Parent Company Only) Financial Information</link:label>
    <link:label id="lab_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Condensed Financial Information of Parent Company Only Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock" xlink:to="lab_us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_b5e313f7-4b06-4923-a3d3-f1e557311bb0_verboseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated amortization on intangible assets</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_9b33c63e-fe4e-4753-b989-2bcf7a5f7f19_negatedLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Less: accumulated amortization</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_label_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Assets, Accumulated Amortization</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:to="lab_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_RangeMember_9da4b29d-9712-4b93-b47c-bd92ad392514_terseLabel_en-US" xlink:label="lab_srt_RangeMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statistical Measurement [Domain]</link:label>
    <link:label id="lab_srt_RangeMember_label_en-US" xlink:label="lab_srt_RangeMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statistical Measurement [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_RangeMember" xlink:to="lab_srt_RangeMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_SpecialtyVehicleMember_5b598956-5101-4bc9-bc2c-0f0be94ff8fa_terseLabel_en-US" xlink:label="lab_source_SpecialtyVehicleMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Specialty vehicle</link:label>
    <link:label id="lab_source_SpecialtyVehicleMember_label_en-US" xlink:label="lab_source_SpecialtyVehicleMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Specialty Vehicle [Member]</link:label>
    <link:label id="lab_source_SpecialtyVehicleMember_documentation_en-US" xlink:label="lab_source_SpecialtyVehicleMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Class of financing receivables related to specialty vehicle loans in the auto and light truck portfolio.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_SpecialtyVehicleMember" xlink:href="source-20211231.xsd#source_SpecialtyVehicleMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_SpecialtyVehicleMember" xlink:to="lab_source_SpecialtyVehicleMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LoansAvailableForRepurchase_f55bfda7-f3e8-46a2-b8aa-0a37185bfd9c_terseLabel_en-US" xlink:label="lab_source_LoansAvailableForRepurchase" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans available for repurchase</link:label>
    <link:label id="lab_source_LoansAvailableForRepurchase_label_en-US" xlink:label="lab_source_LoansAvailableForRepurchase" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans Available for Repurchase</link:label>
    <link:label id="lab_source_LoansAvailableForRepurchase_documentation_en-US" xlink:label="lab_source_LoansAvailableForRepurchase" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the loans available for repurchase under the Government National Mortgage Association optional repurchase programs with the offsetting liability recorded within other short-term borrowings.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LoansAvailableForRepurchase" xlink:href="source-20211231.xsd#source_LoansAvailableForRepurchase"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LoansAvailableForRepurchase" xlink:to="lab_source_LoansAvailableForRepurchase" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk_82be8abf-d381-4a2e-a340-0e2897764183_terseLabel_en-US" xlink:label="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of methods to assess credit risk</link:label>
    <link:label id="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk_label_en-US" xlink:label="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases Receivable, Number of Methods to Assess Credit Risk</link:label>
    <link:label id="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk_documentation_en-US" xlink:label="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the number of methods to assess credit risk of loans and leases receivables.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk" xlink:href="source-20211231.xsd#source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk" xlink:to="lab_source_LoansAndLeasesReceivableNumberOfMethodsToAssessCreditRisk" xlink:type="arc" order="1"/>
    <link:label id="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure_52808846-d7ca-4acd-a8c3-3346f47c3346_terseLabel_en-US" xlink:label="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued income and other assets</link:label>
    <link:label id="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure_label_en-US" xlink:label="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued Income and Other Assets, Fair Value Disclosure</link:label>
    <link:label id="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure_documentation_en-US" xlink:label="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the portion of the accrued income and other assets balance sheet assertion valued at fair value.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_AccruedIncomeAndOtherAssetsFairValueDisclosure" xlink:href="source-20211231.xsd#source_AccruedIncomeAndOtherAssetsFairValueDisclosure"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_AccruedIncomeAndOtherAssetsFairValueDisclosure" xlink:to="lab_source_AccruedIncomeAndOtherAssetsFairValueDisclosure" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome_fbd23179-1662-4643-97e4-770d167c8f74_negatedLabel_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tax-exempt interest income (as a percent)</link:label>
    <link:label id="lab_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome_label_en-US" xlink:label="lab_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome" xlink:to="lab_us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SegmentReportingPolicyPolicyTextBlock_574ff4b5-c0f9-4d59-aeda-128601d9ea4c_terseLabel_en-US" xlink:label="lab_us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Segment Information</link:label>
    <link:label id="lab_us-gaap_SegmentReportingPolicyPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Segment Reporting, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentReportingPolicyPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:to="lab_us-gaap_SegmentReportingPolicyPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OffsettingAssetsTableTextBlock_359a27cd-c1ef-4b18-bd30-95f4af6f0592_terseLabel_en-US" xlink:label="lab_us-gaap_OffsettingAssetsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of offsetting of financial assets and derivative assets</link:label>
    <link:label id="lab_us-gaap_OffsettingAssetsTableTextBlock_label_en-US" xlink:label="lab_us-gaap_OffsettingAssetsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Offsetting Assets [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingAssetsTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OffsettingAssetsTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OffsettingAssetsTableTextBlock" xlink:to="lab_us-gaap_OffsettingAssetsTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ImpairedLoansMeasurementInput_41692400-545a-4b89-9955-cccb38f627cc_terseLabel_en-US" xlink:label="lab_source_ImpairedLoansMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impaired loans unobservable inputs (as a percent)</link:label>
    <link:label id="lab_source_ImpairedLoansMeasurementInput_label_en-US" xlink:label="lab_source_ImpairedLoansMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impaired Loans Measurement Input</link:label>
    <link:label id="lab_source_ImpairedLoansMeasurementInput_documentation_en-US" xlink:label="lab_source_ImpairedLoansMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Value of input used to measure impaired loans.</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract_f78b0538-23d8-4c90-b192-a5a5638634d5_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross realized gains and losses</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityIncorporationStateCountryCode_b6d50ba0-2282-42da-8b48-5c5e9e74267a_terseLabel_en-US" xlink:label="lab_dei_EntityIncorporationStateCountryCode" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Incorporation, State or Country Code</link:label>
    <link:label id="lab_dei_EntityIncorporationStateCountryCode_label_en-US" xlink:label="lab_dei_EntityIncorporationStateCountryCode" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Incorporation, State or Country Code</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityIncorporationStateCountryCode" xlink:to="lab_dei_EntityIncorporationStateCountryCode" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_UndistributedEarnings_3bfd620b-0234-448a-a707-028b093b5ad7_terseLabel_en-US" xlink:label="lab_us-gaap_UndistributedEarnings" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Undistributed earnings allocated to common stock</link:label>
    <link:label id="lab_us-gaap_UndistributedEarnings_label_en-US" xlink:label="lab_us-gaap_UndistributedEarnings" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Undistributed Earnings, Basic</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UndistributedEarnings" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UndistributedEarnings"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_UndistributedEarnings" xlink:to="lab_us-gaap_UndistributedEarnings" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm_c88561de-150c-4255-843a-e8caf727f74e_terseLabel_en-US" xlink:label="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current expected credit losses initial loss forecast term</link:label>
    <link:label id="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm_label_en-US" xlink:label="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">CurrentExpectedCreditLossesInitialLossForecastTerm</link:label>
    <link:label id="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm_documentation_en-US" xlink:label="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current expected credit losses initial loss forecast term</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CurrentExpectedCreditLossesInitialLossForecastTerm" xlink:href="source-20211231.xsd#source_CurrentExpectedCreditLossesInitialLossForecastTerm"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CurrentExpectedCreditLossesInitialLossForecastTerm" xlink:to="lab_source_CurrentExpectedCreditLossesInitialLossForecastTerm" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification_2605a5b8-5b53-4626-916d-aecf2f08e761_terseLabel_en-US" xlink:label="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liability for repurchases</link:label>
    <link:label id="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification_label_en-US" xlink:label="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liability for Estimated Losses on Repurchase and Indemnification</link:label>
    <link:label id="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification_documentation_en-US" xlink:label="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liability for estimated losses on mortgage loan repurchases and indemnification.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification" xlink:href="source-20211231.xsd#source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification" xlink:to="lab_source_LiabilityForEstimatedLossesOnRepurchaseAndIndemnification" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeCollateralRightToReclaimSecurities_10384d9e-313d-4f67-9ed2-d41b476ca38a_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeCollateralRightToReclaimSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial instruments</link:label>
    <link:label id="lab_us-gaap_DerivativeCollateralRightToReclaimSecurities_label_en-US" xlink:label="lab_us-gaap_DerivativeCollateralRightToReclaimSecurities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative, Collateral, Right to Reclaim Securities</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimSecurities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeCollateralRightToReclaimSecurities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeCollateralRightToReclaimSecurities" xlink:to="lab_us-gaap_DerivativeCollateralRightToReclaimSecurities" xlink:type="arc" order="1"/>
    <link:label id="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards_123d73cd-e054-4bde-b6f4-c40ba590b053_terseLabel_en-US" xlink:label="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Issuance of common shares per stock based compensation awards, shares</link:label>
    <link:label id="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards_label_en-US" xlink:label="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock Issued During Period, Shares Stock Based Compensation Awards</link:label>
    <link:label id="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards_documentation_en-US" xlink:label="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of shares issued during the period as a result of stock based compensation awards including employee stock ownership plan (ESOP) and employee stock purchase plan (ESPP).</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards" xlink:href="source-20211231.xsd#source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards" xlink:to="lab_source_StockIssuedDuringPeriodSharesStockBasedCompensationAwards" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CompensationAndRetirementDisclosureAbstract_b06e2cb9-99f3-4579-afe9-5e9c0298f5ca_terseLabel_en-US" xlink:label="lab_us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Benefits [Abstract]</link:label>
    <link:label id="lab_us-gaap_CompensationAndRetirementDisclosureAbstract_label_en-US" xlink:label="lab_us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Benefits [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CompensationAndRetirementDisclosureAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:to="lab_us-gaap_CompensationAndRetirementDisclosureAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityFileNumber_112c9cfa-a65e-439c-8baa-cdc2336dc164_terseLabel_en-US" xlink:label="lab_dei_EntityFileNumber" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity File Number</link:label>
    <link:label id="lab_dei_EntityFileNumber_label_en-US" xlink:label="lab_dei_EntityFileNumber" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity File Number</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityFileNumber"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityFileNumber" xlink:to="lab_dei_EntityFileNumber" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract_738a6ef9-2df4-42c5-9df7-2d3566b77885_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract_label_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract" xlink:to="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableImpairedLineItems_724d501d-7c8b-41ce-b9b5-a69dcb665f96_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableImpairedLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impaired loans and leases</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableImpairedLineItems_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableImpairedLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Impaired [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableImpairedLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableImpairedLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableImpairedLineItems" xlink:to="lab_us-gaap_FinancingReceivableImpairedLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RetirementPlanNameDomain_518e97cf-2577-4882-a455-0959975e6fb8_terseLabel_en-US" xlink:label="lab_us-gaap_RetirementPlanNameDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Name [Domain]</link:label>
    <link:label id="lab_us-gaap_RetirementPlanNameDomain_label_en-US" xlink:label="lab_us-gaap_RetirementPlanNameDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retirement Plan Name [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetirementPlanNameDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RetirementPlanNameDomain" xlink:to="lab_us-gaap_RetirementPlanNameDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ServicingAssetCarryingValueNet_c0a36019-ab85-4d6e-a575-4ef802727394_totalLabel_en-US" xlink:label="lab_source_ServicingAssetCarryingValueNet" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net carrying value of mortgage servicing rights at end of period</link:label>
    <link:label id="lab_source_ServicingAssetCarryingValueNet_label_en-US" xlink:label="lab_source_ServicingAssetCarryingValueNet" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset Carrying Value, Net</link:label>
    <link:label id="lab_source_ServicingAssetCarryingValueNet_documentation_en-US" xlink:label="lab_source_ServicingAssetCarryingValueNet" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the carrying value of mortgage servicing assets, net of valuation allowance, related to mortgage servicing assets.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ServicingAssetCarryingValueNet" xlink:href="source-20211231.xsd#source_ServicingAssetCarryingValueNet"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ServicingAssetCarryingValueNet" xlink:to="lab_source_ServicingAssetCarryingValueNet" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue_fab05d50-b1e5-4bbf-b9c3-6e0116dcd331_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Due after ten years</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_source_OtherLongTermDebtMember_22cc014c-8d31-4f35-99be-1a6e8188f40d_terseLabel_en-US" xlink:label="lab_source_OtherLongTermDebtMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other long-term debt</link:label>
    <link:label id="lab_source_OtherLongTermDebtMember_label_en-US" xlink:label="lab_source_OtherLongTermDebtMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Long Term Debt [Member]</link:label>
    <link:label id="lab_source_OtherLongTermDebtMember_documentation_en-US" xlink:label="lab_source_OtherLongTermDebtMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to other long-term debt which is not elsewhere specified.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_OtherLongTermDebtMember" xlink:href="source-20211231.xsd#source_OtherLongTermDebtMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_OtherLongTermDebtMember" xlink:to="lab_source_OtherLongTermDebtMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ValuationTechniqueDomain_f04f643a-d868-4f8a-a30f-78d50d7a41ce_terseLabel_en-US" xlink:label="lab_us-gaap_ValuationTechniqueDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Approach and Technique [Domain]</link:label>
    <link:label id="lab_us-gaap_ValuationTechniqueDomain_label_en-US" xlink:label="lab_us-gaap_ValuationTechniqueDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Approach and Technique [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ValuationTechniqueDomain" xlink:to="lab_us-gaap_ValuationTechniqueDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ExecutiveIncentivePlanMember_19d487e4-32fa-45d8-8590-e0e2fa4e6c81_terseLabel_en-US" xlink:label="lab_source_ExecutiveIncentivePlanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Executive Incentive Plan</link:label>
    <link:label id="lab_source_ExecutiveIncentivePlanMember_label_en-US" xlink:label="lab_source_ExecutiveIncentivePlanMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Executive Incentive Plan [Member]</link:label>
    <link:label id="lab_source_ExecutiveIncentivePlanMember_documentation_en-US" xlink:label="lab_source_ExecutiveIncentivePlanMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to the Executive Incentive Plan.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ExecutiveIncentivePlanMember" xlink:href="source-20211231.xsd#source_ExecutiveIncentivePlanMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ExecutiveIncentivePlanMember" xlink:to="lab_source_ExecutiveIncentivePlanMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted_fec476f1-88a3-41cf-a072-3f48a6ebaec4_negatedLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Granted (in shares)</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted_label_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share Based Compensation Arrangement by Share Based Payment Award, Number of Shares Granted</link:label>
    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted_documentation_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the number of shares granted during the period which were available for grant.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" xlink:href="source-20211231.xsd#source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" xlink:to="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_VariableLeaseCost_e17babc4-7ba0-4a54-aa29-ed02e6ce6ce0_terseLabel_en-US" xlink:label="lab_us-gaap_VariableLeaseCost" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable lease cost</link:label>
    <link:label id="lab_us-gaap_VariableLeaseCost_label_en-US" xlink:label="lab_us-gaap_VariableLeaseCost" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Lease, Cost</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableLeaseCost" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableLeaseCost"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_VariableLeaseCost" xlink:to="lab_us-gaap_VariableLeaseCost" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits_71d00aa9-57b4-4f5c-ac7d-aaba184301e6_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accruals for employee benefits</link:label>
    <link:label id="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits_label_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" xlink:to="lab_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable_a3438441-37a3-4be6-a279-28519126375b_terseLabel_en-US" xlink:label="lab_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Table]</link:label>
    <link:label id="lab_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable_label_en-US" xlink:label="lab_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable" xlink:to="lab_us-gaap_TransferOfCertainFinancialAssetsAccountedForAsSecuredBorrowingsTable" xlink:type="arc" order="1"/>
    <link:label id="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions_2460e00e-ae10-4f85-9056-f23a90bcf186_terseLabel_en-US" xlink:label="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of available-for-sale debt securities</link:label>
    <link:label id="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions_label_en-US" xlink:label="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Available-for-sale, Securities Held, Qualitative Disclosure, Number of Positions</link:label>
    <link:label id="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions_documentation_en-US" xlink:label="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of available-for-sale debt securities held in portfolio.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions" xlink:href="source-20211231.xsd#source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions" xlink:to="lab_source_AvailableforsaleSecuritiesHeldQualitativeDisclosureNumberofPositions" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0b04f849-81b8-4844-8041-eb671251f2de_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Granted (in dollars per share)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_source_VariableInterestEntities_e3cfea9e-2937-477d-a64f-1aa2c5ee34c2_terseLabel_en-US" xlink:label="lab_source_VariableInterestEntities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Interest Entities</link:label>
    <link:label id="lab_source_VariableInterestEntities_label_en-US" xlink:label="lab_source_VariableInterestEntities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Interest Entities</link:label>
    <link:label id="lab_source_VariableInterestEntities_documentation_en-US" xlink:label="lab_source_VariableInterestEntities" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_VariableInterestEntities" xlink:href="source-20211231.xsd#source_VariableInterestEntities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_VariableInterestEntities" xlink:to="lab_source_VariableInterestEntities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MunicipalBondsMember_a4601d32-44ff-4f4e-8da9-479781b43a7c_terseLabel_en-US" xlink:label="lab_us-gaap_MunicipalBondsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Direct placement municipal securities</link:label>
    <link:label id="lab_us-gaap_MunicipalBondsMember_label_en-US" xlink:label="lab_us-gaap_MunicipalBondsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Municipal Bonds [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MunicipalBondsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MunicipalBondsMember" xlink:to="lab_us-gaap_MunicipalBondsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput_a0713cd3-4703-465e-b510-5819af9d8291_terseLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt securities available-for-sale unobservable inputs (as a percent)</link:label>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput_label_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Measurement Input</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:to="lab_us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries_46a47ea2-eeb6-4296-b93c-0d5f8859340b_terseLabel_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairment recoveries (charges)</link:label>
    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries_label_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Allowance for Impairment of Recognized Servicing Assets, Additions (Deductions) for Expenses (Recoveries)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries" xlink:to="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisionsRecoveries" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_ff8bef0d-4a35-4d0f-9fad-307a03cd82f6_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from maturities and paydowns of investment securities available-for-sale</link:label>
    <link:label id="lab_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_label_en-US" xlink:label="lab_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:to="lab_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities" xlink:type="arc" order="1"/>
    <link:label id="lab_source_SuppliesAndCommunicationExpense_b29d920d-cf6a-4ac8-af2e-d11d9db27cef_terseLabel_en-US" xlink:label="lab_source_SuppliesAndCommunicationExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Supplies and communication</link:label>
    <link:label id="lab_source_SuppliesAndCommunicationExpense_label_en-US" xlink:label="lab_source_SuppliesAndCommunicationExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Supplies and Communication Expense</link:label>
    <link:label id="lab_source_SuppliesAndCommunicationExpense_documentation_en-US" xlink:label="lab_source_SuppliesAndCommunicationExpense" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents the amount of expense incurred for supplies and postage. Also includes the amount of expense incurred in the period for communication, which is the exchange of information by several methods.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_SuppliesAndCommunicationExpense" xlink:href="source-20211231.xsd#source_SuppliesAndCommunicationExpense"/>
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    <link:label id="lab_us-gaap_StockOptionMember_c3bd13d8-6856-4b74-9e00-5c0358f72df0_terseLabel_en-US" xlink:label="lab_us-gaap_StockOptionMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock options</link:label>
    <link:label id="lab_us-gaap_StockOptionMember_label_en-US" xlink:label="lab_us-gaap_StockOptionMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity Option [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockOptionMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockOptionMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StockOptionMember" xlink:to="lab_us-gaap_StockOptionMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AssetsAbstract_d5f6a70a-74a5-4077-8209-d6e8d5e6ffaf_terseLabel_en-US" xlink:label="lab_us-gaap_AssetsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ASSETS</link:label>
    <link:label id="lab_us-gaap_AssetsAbstract_label_en-US" xlink:label="lab_us-gaap_AssetsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Assets [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="lab_us-gaap_AssetsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_0ba39b40-6bde-48e0-a2c3-20e23eff7ba8_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2024</link:label>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_label_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-Term Debt, Maturity, Year Three</link:label>
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    <link:label id="lab_us-gaap_LandMember_b7c18e83-2215-4d20-9e78-07a3a44c7571_terseLabel_en-US" xlink:label="lab_us-gaap_LandMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Land</link:label>
    <link:label id="lab_us-gaap_LandMember_label_en-US" xlink:label="lab_us-gaap_LandMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Land [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LandMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LandMember" xlink:to="lab_us-gaap_LandMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_USStatesAndPoliticalSubdivisionsMember_3498b5f1-5449-4630-9d29-aa54b0090f5c_terseLabel_en-US" xlink:label="lab_us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">U.S. States and political subdivisions securities</link:label>
    <link:label id="lab_us-gaap_USStatesAndPoliticalSubdivisionsMember_label_en-US" xlink:label="lab_us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">US States and Political Subdivisions Debt Securities [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
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    <link:label id="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_02a22bc4-332c-4e1b-8dea-d994717e511c_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Financial Instruments</link:label>
    <link:label id="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Instruments and Hedging Activities Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock" xlink:to="lab_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_dc04d24f-f8dc-4ce7-b548-0d7cc6d8b211_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing receivable originated five years or more prior to current fiscal year</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Originated, More than Five Years before Current Fiscal Year</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_d48fb46f-51d1-417d-a2bb-d3c808c26199_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Granted (in shares)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_cceaec6f-8561-4f12-8951-4ac213477136_terseLabel_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Intangible Assets and Goodwill</link:label>
    <link:label id="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill and Intangible Assets Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:to="lab_us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_40fe47e2-3ec6-478a-bc31-43fe65b6cc56_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net proceeds from issuance of treasury stock</link:label>
    <link:label id="lab_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_label_en-US" xlink:label="lab_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:to="lab_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_f97d8623-e804-4418-9618-6e116146c6d2_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Premises and Equipment</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GainLossOnSaleOfMortgageLoans_b43c7438-3d6b-4af6-9bd0-d6a04dc82bd6_negatedLabel_en-US" xlink:label="lab_us-gaap_GainLossOnSaleOfMortgageLoans" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net gains on sale of loans held for sale</link:label>
    <link:label id="lab_us-gaap_GainLossOnSaleOfMortgageLoans_label_en-US" xlink:label="lab_us-gaap_GainLossOnSaleOfMortgageLoans" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gain (Loss) on Sale of Mortgage Loans</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfMortgageLoans" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnSaleOfMortgageLoans"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GainLossOnSaleOfMortgageLoans" xlink:to="lab_us-gaap_GainLossOnSaleOfMortgageLoans" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtInstrumentAxis_157a049e-1e84-489a-9fdf-cf6927db02fd_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentAxis_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentAxis" xlink:to="lab_us-gaap_DebtInstrumentAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommercialRealEstateMember_f1ff9270-d901-4dd9-98e0-0ef53110a7d4_terseLabel_en-US" xlink:label="lab_us-gaap_CommercialRealEstateMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial real estate</link:label>
    <link:label id="lab_us-gaap_CommercialRealEstateMember_label_en-US" xlink:label="lab_us-gaap_CommercialRealEstateMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial Real Estate [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialRealEstateMember"/>
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    <link:label id="lab_us-gaap_MaturityUpTo30DaysMember_07dd2a26-3d07-4bd4-8206-e96f3b423a18_terseLabel_en-US" xlink:label="lab_us-gaap_MaturityUpTo30DaysMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Up to 30 Days</link:label>
    <link:label id="lab_us-gaap_MaturityUpTo30DaysMember_label_en-US" xlink:label="lab_us-gaap_MaturityUpTo30DaysMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maturity Less than 30 Days [Member]</link:label>
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    <link:label id="lab_us-gaap_FinancingReceivablesPeriodPastDueDomain_7ba67969-9678-4227-ba64-b08fef57591b_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Asset, Period Past Due [Domain]</link:label>
    <link:label id="lab_us-gaap_FinancingReceivablesPeriodPastDueDomain_label_en-US" xlink:label="lab_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Asset, Aging [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
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    <link:label id="lab_us-gaap_UnfundedLoanCommitmentMember_0c501d10-6a87-4a0d-9043-f0b044771661_terseLabel_en-US" xlink:label="lab_us-gaap_UnfundedLoanCommitmentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unfunded Loan Commitment</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnfundedLoanCommitmentMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnfundedLoanCommitmentMember"/>
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    <link:label id="lab_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_3dbdaba3-7a29-4f1e-addb-9263b883cd79_terseLabel_en-US" xlink:label="lab_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contingent Liabilities, Commitments, and Financial Instruments with Off-Balance-Sheet Risk</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:to="lab_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets_e390e044-0037-428d-9390-9e450dc6e32e_terseLabel_en-US" xlink:label="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy with Capital Buffer Ratio (as a percent)</link:label>
    <link:label id="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets_label_en-US" xlink:label="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer to Risk Weighted Assets</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets" xlink:href="source-20211231.xsd#source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffertoRiskWeightedAssets"/>
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    <link:label id="lab_source_MandatorilyRedeemableSecuritiesAbstract_cebe383a-24e2-464b-8323-d7be3f015fdc_terseLabel_en-US" xlink:label="lab_source_MandatorilyRedeemableSecuritiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mandatorily redeemable securities</link:label>
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    <link:label id="lab_source_MandatorilyRedeemableSecuritiesAbstract_documentation_en-US" xlink:label="lab_source_MandatorilyRedeemableSecuritiesAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_MandatorilyRedeemableSecuritiesAbstract" xlink:href="source-20211231.xsd#source_MandatorilyRedeemableSecuritiesAbstract"/>
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    <link:label id="lab_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_c74189a3-2922-41d3-917d-95d5ada149eb_terseLabel_en-US" xlink:label="lab_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Related Party [Axis]</link:label>
    <link:label id="lab_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_label_en-US" xlink:label="lab_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Related Party [Axis]</link:label>
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    <link:label id="lab_source_MortgageServicingRightsMember_61c2883c-5e6f-4e22-ae94-f0d58445fcde_terseLabel_en-US" xlink:label="lab_source_MortgageServicingRightsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage servicing rights</link:label>
    <link:label id="lab_source_MortgageServicingRightsMember_label_en-US" xlink:label="lab_source_MortgageServicingRightsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage Servicing Rights [Member]</link:label>
    <link:label id="lab_source_MortgageServicingRightsMember_documentation_en-US" xlink:label="lab_source_MortgageServicingRightsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Details pertaining to mortgage servicing rights.</link:label>
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    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFourYears_ed5fc913-f30c-40fa-88ab-bf776bbedfcc_terseLabel_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFourYears" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2025</link:label>
    <link:label id="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFourYears_label_en-US" xlink:label="lab_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFourYears" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Four</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFourYears" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedFourYears"/>
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    <link:label id="lab_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_055e5df8-7117-41c3-8291-88ec455d6eff_terseLabel_en-US" xlink:label="lab_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Right of use assets obtained in exchange for lease obligation</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_1ab45ba8-23bc-4d97-8faa-9c8a31550c23_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of deferred tax assets and liabilities</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_22b2445c-796f-4fc7-b726-fedade079b23_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maximum base rate of employee basic pay to purchase any dollar amount of stock (as a percent)</link:label>
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    <link:label id="lab_us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale_0802b666-0c51-4217-a2e3-bd41bafe04e3_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from the sales of loans held for sale</link:label>
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    <link:label id="lab_us-gaap_InternalCreditAssessmentDomain_9d8eeb58-2aef-4794-9d3f-8143b67b2c99_terseLabel_en-US" xlink:label="lab_us-gaap_InternalCreditAssessmentDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Internal Credit Assessment [Domain]</link:label>
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    <link:label id="lab_source_AssetImpairmentRecoveries_eba8a6a5-0d69-4849-9fc3-4380559eaca0_negatedTerseLabel_en-US" xlink:label="lab_source_AssetImpairmentRecoveries" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairment recoveries</link:label>
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    <link:label id="lab_source_DeferredTaxAssetsCapitalizedLoanCosts_291918b9-4d6d-431e-a703-3d4ea70f5c45_terseLabel_en-US" xlink:label="lab_source_DeferredTaxAssetsCapitalizedLoanCosts" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Capitalized loan costs</link:label>
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    <link:label id="lab_source_DeferredTaxAssetsCapitalizedLoanCosts_documentation_en-US" xlink:label="lab_source_DeferredTaxAssetsCapitalizedLoanCosts" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount before allocation of valuation allowances of deferred tax asset attributable to deductible capitalized loan costs.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DeferredTaxAssetsCapitalizedLoanCosts" xlink:href="source-20211231.xsd#source_DeferredTaxAssetsCapitalizedLoanCosts"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DeferredTaxAssetsCapitalizedLoanCosts" xlink:to="lab_source_DeferredTaxAssetsCapitalizedLoanCosts" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock_6efd7d11-e1fc-4b40-8314-0d5c5f3b0e1c_terseLabel_en-US" xlink:label="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease Investments Disclosure Text Block</link:label>
    <link:label id="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock_label_en-US" xlink:label="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease Investments Disclosure Text Block [Text Block]</link:label>
    <link:label id="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock_documentation_en-US" xlink:label="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The entire disclosure of lessor entity's leasing arrangements for direct finance and operating leases.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LeaseInvestmentsDisclosureTextBlockTextBlock" xlink:href="source-20211231.xsd#source_LeaseInvestmentsDisclosureTextBlockTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LeaseInvestmentsDisclosureTextBlockTextBlock" xlink:to="lab_source_LeaseInvestmentsDisclosureTextBlockTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_OperatingLeaseRightofUseAssetAmortization_8a0c5d77-9bdf-430d-8e9a-177c54f14a0b_terseLabel_en-US" xlink:label="lab_source_OperatingLeaseRightofUseAssetAmortization" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amortization of right of use assets</link:label>
    <link:label id="lab_source_OperatingLeaseRightofUseAssetAmortization_label_en-US" xlink:label="lab_source_OperatingLeaseRightofUseAssetAmortization" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease Right of Use Asset Amortization</link:label>
    <link:label id="lab_source_OperatingLeaseRightofUseAssetAmortization_documentation_en-US" xlink:label="lab_source_OperatingLeaseRightofUseAssetAmortization" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of amortization expense attributable to right-of-use asset from operating lease.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_OperatingLeaseRightofUseAssetAmortization" xlink:href="source-20211231.xsd#source_OperatingLeaseRightofUseAssetAmortization"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_OperatingLeaseRightofUseAssetAmortization" xlink:to="lab_source_OperatingLeaseRightofUseAssetAmortization" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_USTreasuryAndGovernmentMember_bc48ddd3-f311-495f-a57e-dec7fab5c187_terseLabel_en-US" xlink:label="lab_us-gaap_USTreasuryAndGovernmentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">U.S. Treasury and Federal agencies securities</link:label>
    <link:label id="lab_us-gaap_USTreasuryAndGovernmentMember_label_en-US" xlink:label="lab_us-gaap_USTreasuryAndGovernmentMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">US Treasury and Government [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_USTreasuryAndGovernmentMember" xlink:to="lab_us-gaap_USTreasuryAndGovernmentMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_dfeab584-fe43-4f9d-b041-9b1b1fe7c3f5_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2024</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, Year Three</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_2b547f2d-2cef-41fa-aaa5-c1cfa0e05938_terseLabel_en-US" xlink:label="lab_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unpaid principal balance</link:label>
    <link:label id="lab_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_label_en-US" xlink:label="lab_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Principal Amount Outstanding of Loans Held-in-portfolio</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio" xlink:to="lab_us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_ee7f04bd-991d-4f27-89b0-8a77e05b5fdc_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">90 Days or More Past Due and Accruing</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, 90 Days or More Past Due, Still Accruing</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:to="lab_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LetterofCreditTerm_37ac8acf-26aa-43e0-8d03-faeb955cb347_terseLabel_en-US" xlink:label="lab_source_LetterofCreditTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Letter of credit term</link:label>
    <link:label id="lab_source_LetterofCreditTerm_label_en-US" xlink:label="lab_source_LetterofCreditTerm" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Letter of Credit Term</link:label>
    <link:label id="lab_source_LetterofCreditTerm_documentation_en-US" xlink:label="lab_source_LetterofCreditTerm" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the time period for repayment of funds borrowed under the letter of credit.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LetterofCreditTerm" xlink:href="source-20211231.xsd#source_LetterofCreditTerm"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LetterofCreditTerm" xlink:to="lab_source_LetterofCreditTerm" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DepositLiabilitiesDisclosureTextBlock_28d0c38d-3bcc-436e-87e9-f14e16d30e28_terseLabel_en-US" xlink:label="lab_source_DepositLiabilitiesDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deposits</link:label>
    <link:label id="lab_source_DepositLiabilitiesDisclosureTextBlock_label_en-US" xlink:label="lab_source_DepositLiabilitiesDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deposit Liabilities Disclosure [Text Block]</link:label>
    <link:label id="lab_source_DepositLiabilitiesDisclosureTextBlock_documentation_en-US" xlink:label="lab_source_DepositLiabilitiesDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The entire disclosure for deposit liabilities including data and tables. It may include a description of the entity's deposit liabilities, the aggregate amount of time deposits (including certificates of deposit) in denominations of $250,000 or more at the balance sheet date; the aggregate amount of any demand deposits that have been reclassified as loan balances, such as overdrafts, at the balance sheet date; deposits that are received on terms other than those in the normal course of business, the amount of accrued interest on deposit liabilities; securities, mortgage loans or other financial instruments that serve as collateral for deposits; for time deposits having a remaining term of more than one year, the aggregate amount of maturities for each of the five years following the balance sheet date; and the weighted average interest rate for all deposit liabilities held by the entity.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DepositLiabilitiesDisclosureTextBlock" xlink:href="source-20211231.xsd#source_DepositLiabilitiesDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DepositLiabilitiesDisclosureTextBlock" xlink:to="lab_source_DepositLiabilitiesDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1_80e0e176-7473-43fa-9f06-e054a1ee6b6c_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:to="lab_us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_0cd804a2-e771-4d1e-8c5e-639913f12793_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2026</link:label>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_label_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-Term Debt, Maturity, Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:to="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DefinedContributionPlanCostRecognized_a0379144-1a44-4003-beca-23ead6000656_terseLabel_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanCostRecognized" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contribution expense</link:label>
    <link:label id="lab_us-gaap_DefinedContributionPlanCostRecognized_label_en-US" xlink:label="lab_us-gaap_DefinedContributionPlanCostRecognized" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Defined Contribution Plan, Cost</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanCostRecognized" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedContributionPlanCostRecognized"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DefinedContributionPlanCostRecognized" xlink:to="lab_us-gaap_DefinedContributionPlanCostRecognized" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths_ee49d7fc-ace4-45cd-850f-0fea17351380_terseLabel_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">4-6 months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths_label_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual Maturities, Time Deposits, $250,000 or More, Three Months Through Six Months</link:label>
    <link:label id="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths_documentation_en-US" xlink:label="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The amount of contractual maturities of domestic and foreign time deposits (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more, for the period from three months through six months after the balance sheet date.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths" xlink:href="source-20211231.xsd#source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths" xlink:to="lab_source_ContractualMaturitiesTimeDeposits250000orMoreThreeMonthsThroughSixMonths" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_b0fa0508-97df-4f84-8338-c0d3097508ef_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Shares</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingLeasePayments_afb41603-6440-4ec0-9002-518f11155812_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasePayments" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating cash flows from operating leases</link:label>
    <link:label id="lab_us-gaap_OperatingLeasePayments_label_en-US" xlink:label="lab_us-gaap_OperatingLeasePayments" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease, Payments</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeasePayments"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasePayments" xlink:to="lab_us-gaap_OperatingLeasePayments" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_e0bf9c22-f179-4dff-a4b9-af00d02d1fed_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Shares authorized</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_adddafce-9d45-418b-b71c-ab7dd9daa352_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromRepaymentsOfShortTermDebt" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in short-term borrowings</link:label>
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    <link:label id="lab_us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_83aec80b-ca83-46ab-b88a-4bb46d8b2bfd_verboseLabel_en-US" xlink:label="lab_us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other investments</link:label>
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    <link:label id="lab_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_81bd0421-4dd6-405d-a662-d0e7ae7adb26_totalLabel_en-US" xlink:label="lab_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net interest income after provision for credit losses</link:label>
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    <link:label id="lab_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_b85e48f0-4518-4492-895e-e6dad46e8596_terseLabel_en-US" xlink:label="lab_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liabilities:</link:label>
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    <link:label id="lab_source_MinimumInitialLeaseTermforRecordingRightofUseAssetandLeaseLiability_2e1bbb08-6a6c-4289-962b-d9f486faf503_terseLabel_en-US" xlink:label="lab_source_MinimumInitialLeaseTermforRecordingRightofUseAssetandLeaseLiability" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum initial lease term for recording right of use asset and lease liability</link:label>
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    <link:label id="lab_source_MinimumInitialLeaseTermforRecordingRightofUseAssetandLeaseLiability_documentation_en-US" xlink:label="lab_source_MinimumInitialLeaseTermforRecordingRightofUseAssetandLeaseLiability" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum initial lease term for recording a right of use asset and lease liability in the Consolidated Statements of Financial Condition for operating lease obligations.</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesAndStockholdersEquity_051ab7d9-79e9-48ad-9644-ca5103e64291_totalLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesAndStockholdersEquity" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total liabilities and equity</link:label>
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    <link:label id="lab_us-gaap_ResidentialRealEstateMember_93264c7a-7345-4f6b-a15e-5f761cde6049_terseLabel_en-US" xlink:label="lab_us-gaap_ResidentialRealEstateMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Residential real estate and home equity</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ResidentialRealEstateMember" xlink:to="lab_us-gaap_ResidentialRealEstateMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_b45c5782-d884-4f8e-a395-1b313ab79ef6_totalLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessor, Operating Lease, Payments to be Received</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceived"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceived" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_64ce08e1-7fd6-4f09-8968-ee3c9692cdf2_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2026</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, Year Five</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_7320f2bd-1bda-4999-90f8-b8659321c815_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing receivable originated three years prior to current fiscal year</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear" xlink:to="lab_us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue_3ab49964-efea-4b33-b318-2a1feebc062f_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Due after five years through ten years</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_source_StrategicDeploymentIncentivePlanMember_37ba6d01-36a7-4b21-ab21-30df436227b9_terseLabel_en-US" xlink:label="lab_source_StrategicDeploymentIncentivePlanMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Strategic Deployment Incentive Plan</link:label>
    <link:label id="lab_source_StrategicDeploymentIncentivePlanMember_label_en-US" xlink:label="lab_source_StrategicDeploymentIncentivePlanMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Strategic Deployment Incentive Plan [Member]</link:label>
    <link:label id="lab_source_StrategicDeploymentIncentivePlanMember_documentation_en-US" xlink:label="lab_source_StrategicDeploymentIncentivePlanMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to the Strategic Deployment Incentive Plan.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_StrategicDeploymentIncentivePlanMember" xlink:href="source-20211231.xsd#source_StrategicDeploymentIncentivePlanMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_StrategicDeploymentIncentivePlanMember" xlink:to="lab_source_StrategicDeploymentIncentivePlanMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection_2cbea63a-e63e-4265-9f7c-551976f92bba_totalLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Amount</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection_label_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" xlink:to="lab_us-gaap_DerivativeLiabilityFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OffsettingLiabilitiesTable_1266c6f0-190c-4e42-b45b-520452b53f96_terseLabel_en-US" xlink:label="lab_us-gaap_OffsettingLiabilitiesTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Offsetting Liabilities [Table]</link:label>
    <link:label id="lab_us-gaap_OffsettingLiabilitiesTable_label_en-US" xlink:label="lab_us-gaap_OffsettingLiabilitiesTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Offsetting Liabilities [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingLiabilitiesTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OffsettingLiabilitiesTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OffsettingLiabilitiesTable" xlink:to="lab_us-gaap_OffsettingLiabilitiesTable" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable_4331f23f-128b-4db8-a119-f7a745dae0db_terseLabel_en-US" xlink:label="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule Of Available For Sale Debt Securities [Table]</link:label>
    <link:label id="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable_label_en-US" xlink:label="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule Of Available For Sale Debt Securities [Table]</link:label>
    <link:label id="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable_documentation_en-US" xlink:label="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule Of Available For Sale Debt Securities [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ScheduleOfAvailableForSaleDebtSecuritiesTable" xlink:href="source-20211231.xsd#source_ScheduleOfAvailableForSaleDebtSecuritiesTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ScheduleOfAvailableForSaleDebtSecuritiesTable" xlink:to="lab_source_ScheduleOfAvailableForSaleDebtSecuritiesTable" xlink:type="arc" order="1"/>
    <link:label id="lab_source_RepossessionsMember_f8e6325f-4abb-4c48-a1ba-ff3630b354fd_terseLabel_en-US" xlink:label="lab_source_RepossessionsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repossessions</link:label>
    <link:label id="lab_source_RepossessionsMember_label_en-US" xlink:label="lab_source_RepossessionsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repossessions [Member]</link:label>
    <link:label id="lab_source_RepossessionsMember_documentation_en-US" xlink:label="lab_source_RepossessionsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Details pertaining to repossessions of asset.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_RepossessionsMember" xlink:href="source-20211231.xsd#source_RepossessionsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_RepossessionsMember" xlink:to="lab_source_RepossessionsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AssetsHeldInTrust_e93b6ce3-fae5-4bb5-b5e7-028100ff9e37_terseLabel_en-US" xlink:label="lab_us-gaap_AssetsHeldInTrust" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Funds held in trust</link:label>
    <link:label id="lab_us-gaap_AssetsHeldInTrust_label_en-US" xlink:label="lab_us-gaap_AssetsHeldInTrust" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Assets Held-in-trust</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsHeldInTrust" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsHeldInTrust"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AssetsHeldInTrust" xlink:to="lab_us-gaap_AssetsHeldInTrust" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShortTermDebtTypeDomain_8d953f46-d0de-42cf-b41c-d7d206a89d22_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermDebtTypeDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt, Type [Domain]</link:label>
    <link:label id="lab_us-gaap_ShortTermDebtTypeDomain_label_en-US" xlink:label="lab_us-gaap_ShortTermDebtTypeDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt, Type [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain" xlink:to="lab_us-gaap_ShortTermDebtTypeDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance_032d1c79-79a2-46b9-b1d7-f7a74e16fb03_negatedPeriodStartLabel_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance" xlink:role="http://www.xbrl.org/2009/role/negatedPeriodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance at the beginning of the period</link:label>
    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance_880bc81a-41c0-4ab8-9b96-28b7bb08d564_negatedPeriodEndLabel_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance" xlink:role="http://www.xbrl.org/2009/role/negatedPeriodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance at the end of the period</link:label>
    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance_label_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Allowance for Impairment of Recognized Servicing Assets, Balance</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance" xlink:to="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance" xlink:type="arc" order="1"/>
    <link:label id="lab_source_PPPLoanOriginations_353e72f1-e24b-483e-8e4b-6d6657330485_terseLabel_en-US" xlink:label="lab_source_PPPLoanOriginations" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPP loan originations</link:label>
    <link:label id="lab_source_PPPLoanOriginations_label_en-US" xlink:label="lab_source_PPPLoanOriginations" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPPLoanOriginations</link:label>
    <link:label id="lab_source_PPPLoanOriginations_documentation_en-US" xlink:label="lab_source_PPPLoanOriginations" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPP loan originations</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_PPPLoanOriginations" xlink:href="source-20211231.xsd#source_PPPLoanOriginations"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_PPPLoanOriginations" xlink:to="lab_source_PPPLoanOriginations" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalToAverageAssets_34da4d09-99eb-4553-8c5f-3d4c7acdccc4_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Actual Ratio (as a percent)</link:label>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalToAverageAssets_label_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Tier One Leverage Capital Ratio, Actual</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TierOneLeverageCapitalToAverageAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:to="lab_us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_6cee5cbc-0cac-4fd5-bc62-7a5a308a5852_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating activities:</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:to="lab_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OperatingLeasesIncomeStatementDepreciationExpenseOnPropertySubjectToOrHeldForLease_ad8fea5d-abae-4b13-b615-b8a7bde9dcb4_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasesIncomeStatementDepreciationExpenseOnPropertySubjectToOrHeldForLease" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Depreciation - leased equipment</link:label>
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    <link:label id="lab_us-gaap_EarningsPerShareTextBlock_ca33c091-89ea-44ba-88fa-ac70814cfb62_terseLabel_en-US" xlink:label="lab_us-gaap_EarningsPerShareTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Earnings Per Share</link:label>
    <link:label id="lab_us-gaap_EarningsPerShareTextBlock_label_en-US" xlink:label="lab_us-gaap_EarningsPerShareTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Earnings Per Share [Text Block]</link:label>
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    <link:label id="lab_us-gaap_TreasuryStockValueAcquiredCostMethod_d917d390-a4e2-46ae-900b-bd19dd699e83_negatedLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cost of 713,132, 166,446, and 325,787 shares of common stock acquired for treasury for 2021, 2020 and 2019, respectively</link:label>
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    <link:label id="lab_source_RecoveryOfVariableLeaseCost_4ac7494e-bb1c-440e-95aa-2a43c4eca297_negatedTerseLabel_en-US" xlink:label="lab_source_RecoveryOfVariableLeaseCost" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recovery of variable lease cost</link:label>
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    <link:label id="lab_source_RecoveryOfVariableLeaseCost_documentation_en-US" xlink:label="lab_source_RecoveryOfVariableLeaseCost" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recovery of variable lease cost</link:label>
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    <link:label id="lab_us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets_61116790-a017-432b-8574-71912d74ba26_terseLabel_en-US" xlink:label="lab_us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage loan contractual servicing fees</link:label>
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    <link:label id="lab_us-gaap_StandbyLettersOfCreditMember_4cac3ff0-f733-423f-b8d6-fd8f8d0a02ad_terseLabel_en-US" xlink:label="lab_us-gaap_StandbyLettersOfCreditMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Standby letters of credit</link:label>
    <link:label id="lab_us-gaap_StandbyLettersOfCreditMember_label_en-US" xlink:label="lab_us-gaap_StandbyLettersOfCreditMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Standby Letters of Credit [Member]</link:label>
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    <link:label id="lab_srt_MinimumMember_188ac8f6-92e1-416f-9968-b7a19ef0ca36_terseLabel_en-US" xlink:label="lab_srt_MinimumMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum</link:label>
    <link:label id="lab_srt_MinimumMember_label_en-US" xlink:label="lab_srt_MinimumMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
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    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_0da73b31-81c8-49a0-ad50-d786aa86e63b_negatedLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
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    <link:label id="lab_us-gaap_LoanPurchaseCommitmentsMember_aca2de3f-5711-4a3e-8d67-abe14c0da6a9_terseLabel_en-US" xlink:label="lab_us-gaap_LoanPurchaseCommitmentsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan commitments</link:label>
    <link:label id="lab_us-gaap_LoanPurchaseCommitmentsMember_label_en-US" xlink:label="lab_us-gaap_LoanPurchaseCommitmentsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan Purchase Commitments [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanPurchaseCommitmentsMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoanPurchaseCommitmentsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LoanPurchaseCommitmentsMember" xlink:to="lab_us-gaap_LoanPurchaseCommitmentsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_InternallyAssignedGrade1To6Member_71de8607-153e-4668-81e8-176bb6e0bbbc_terseLabel_en-US" xlink:label="lab_source_InternallyAssignedGrade1To6Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Credit Quality Grades 1-6</link:label>
    <link:label id="lab_source_InternallyAssignedGrade1To6Member_label_en-US" xlink:label="lab_source_InternallyAssignedGrade1To6Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Internally Assigned Grade 1 to 6 [Member]</link:label>
    <link:label id="lab_source_InternallyAssignedGrade1To6Member_documentation_en-US" xlink:label="lab_source_InternallyAssignedGrade1To6Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents internally generated quality grades indicating the upper end of quality rankings, such that a credit quality grade of 1 indicates a superior credit quality.</link:label>
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    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_90b2ec62-cb14-4b55-8210-617ea2b8c338_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2023</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, to be Paid, Year Two</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:to="lab_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LiabilitiesFairValueDisclosure_21a33c67-822c-4850-b7e4-5fa92a42f7f6_terseLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total</link:label>
    <link:label id="lab_us-gaap_LiabilitiesFairValueDisclosure_label_en-US" xlink:label="lab_us-gaap_LiabilitiesFairValueDisclosure" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial and Nonfinancial Liabilities, Fair Value Disclosure</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosure" xlink:to="lab_us-gaap_LiabilitiesFairValueDisclosure" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_af0c68a1-8ff7-4205-8544-4cd80aae99af_totalLabel_en-US" xlink:label="lab_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income before income taxes</link:label>
    <link:label id="lab_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_1143d22a-b0ca-4f17-8ea0-730c73d9545d_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income before income taxes</link:label>
    <link:label id="lab_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_label_en-US" xlink:label="lab_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
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    <link:label id="lab_source_DefinedContributionPlanNumberofSharesofEquitySecuritiesIssuedbyEmployerandRelatedPartiesIncludedinPlanAssets_c58dfb1b-491e-4926-8fda-daf3e496dbb0_terseLabel_en-US" xlink:label="lab_source_DefinedContributionPlanNumberofSharesofEquitySecuritiesIssuedbyEmployerandRelatedPartiesIncludedinPlanAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock held in relation to employee benefit plans (in shares)</link:label>
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    <link:label id="lab_source_DefinedContributionPlanNumberofSharesofEquitySecuritiesIssuedbyEmployerandRelatedPartiesIncludedinPlanAssets_documentation_en-US" xlink:label="lab_source_DefinedContributionPlanNumberofSharesofEquitySecuritiesIssuedbyEmployerandRelatedPartiesIncludedinPlanAssets" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The number of employer shares or related party shares included in plan assets.</link:label>
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    <link:label id="lab_us-gaap_PriorPeriodReclassificationAdjustmentDescription_565b5586-0503-4f48-9984-b65b5e49b100_terseLabel_en-US" xlink:label="lab_us-gaap_PriorPeriodReclassificationAdjustmentDescription" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reclassifications</link:label>
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    <link:label id="lab_source_DefinedContributionPlanDiscretionaryEmployerMatchLevelTwo_54db12f1-5bda-4912-b979-ccbbea572434_terseLabel_en-US" xlink:label="lab_source_DefinedContributionPlanDiscretionaryEmployerMatchLevelTwo" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employer's matching contribution on the next 2% of employee contribution (as a percent)</link:label>
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    <link:label id="lab_us-gaap_LoansAndLeasesReceivableRealEstateAcquiredThroughForeclosurePolicy_82794af4-b679-4cfa-8e5b-988305404917_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableRealEstateAcquiredThroughForeclosurePolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Real Estate</link:label>
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    <link:label id="lab_us-gaap_DepositsSavingsDeposits_e00b90eb-b533-4663-b7e5-be62cced762d_terseLabel_en-US" xlink:label="lab_us-gaap_DepositsSavingsDeposits" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Savings</link:label>
    <link:label id="lab_us-gaap_DepositsSavingsDeposits_label_en-US" xlink:label="lab_us-gaap_DepositsSavingsDeposits" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deposits, Savings Deposits</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsSavingsDeposits" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DepositsSavingsDeposits"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DepositsSavingsDeposits" xlink:to="lab_us-gaap_DepositsSavingsDeposits" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableRelatedParties_17147ab8-013a-4252-ba25-77bf93efcc75_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableRelatedParties" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan to related parties</link:label>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableRelatedParties_label_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableRelatedParties" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases Receivable, Related Parties</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LoansAndLeasesReceivableRelatedParties" xlink:to="lab_us-gaap_LoansAndLeasesReceivableRelatedParties" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_f1970750-32d7-4903-a432-04e9e123d431_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2025</link:label>
    <link:label id="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_label_en-US" xlink:label="lab_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long-Term Debt, Maturity, Year Four</link:label>
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    <link:label id="lab_source_StockIssuedDuringPeriodValueStockBasedCompensationAwards_e508bdea-4c07-440f-9ba0-5267afc06140_verboseLabel_en-US" xlink:label="lab_source_StockIssuedDuringPeriodValueStockBasedCompensationAwards" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Issuance of 63,527, 46,089, and 51,533 common shares under stock based compensation awards for 2021, 2020 and 2019, respectively</link:label>
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    <link:label id="lab_us-gaap_RevenueRecognitionPolicyTextBlock_7320eebd-f7ac-433e-8f8a-2077c3fc8ca2_terseLabel_en-US" xlink:label="lab_us-gaap_RevenueRecognitionPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Revenue Recognition</link:label>
    <link:label id="lab_us-gaap_RevenueRecognitionPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_RevenueRecognitionPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Revenue [Policy Text Block]</link:label>
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    <link:label id="lab_us-gaap_DebtDisclosureTextBlock_8b71565e-7086-4c90-9086-919d989621d1_terseLabel_en-US" xlink:label="lab_us-gaap_DebtDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Borrowed Funds And Mandatorily Redeemable Securities</link:label>
    <link:label id="lab_us-gaap_DebtDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_DebtDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Disclosure [Text Block]</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_100ee803-cc5c-4314-8d06-86bdcd5cedfa_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of income tax expense</link:label>
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    <link:label id="lab_us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal_608a4ff7-8982-4402-9b4f-af53be838eea_terseLabel_en-US" xlink:label="lab_us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">(Recovery of) provision on unfunded loan commitments</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue_c39088ab-1faa-43e0-b87e-6ea43feb8055_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Due in one year or less</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate_f5a42501-da4a-4ba2-9924-375319efb21b_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Percentage of the discount fair market value of common stock as on the offering date or the market value as on the purchase date (as a percent)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date</link:label>
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    <link:label id="lab_us-gaap_FairValueInputsLevel3Member_0d013071-a1cf-416b-9079-8f6719a459f4_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueInputsLevel3Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Level 3</link:label>
    <link:label id="lab_us-gaap_FairValueInputsLevel3Member_label_en-US" xlink:label="lab_us-gaap_FairValueInputsLevel3Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Inputs, Level 3 [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
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    <link:label id="lab_us-gaap_PaymentsOfDividendsCommonStock_da296652-f18a-499b-8912-b358430dde64_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsOfDividendsCommonStock" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash dividends paid on common stock</link:label>
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    <link:label id="lab_us-gaap_LesseeLeasesPolicyTextBlock_987fcbef-36d7-4c98-b63b-e7c05faa8793_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeLeasesPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease Commitments</link:label>
    <link:label id="lab_us-gaap_LesseeLeasesPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_LesseeLeasesPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Leases [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeasesPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeasesPolicyTextBlock"/>
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    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_b5356222-6d77-4124-ae81-48e002736cb3_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated other comprehensive (loss) income</link:label>
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    <link:label id="lab_us-gaap_ServicingAssetsAtAmortizedValueTable_cd0268f3-ebc2-47b9-b0b0-7df7bdc1a05f_terseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetsAtAmortizedValueTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Servicing Rights at Amortized Value [Table]</link:label>
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    <link:label id="lab_us-gaap_NumberOfReportableSegments_8068658c-0093-49f9-9c6f-40abd2bd21e9_terseLabel_en-US" xlink:label="lab_us-gaap_NumberOfReportableSegments" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of business segments aggregated as reportable operating segments</link:label>
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    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_52dfc975-a43b-4ea1-81c6-59ad7215ef4c_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2025</link:label>
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    <link:label id="lab_source_RepossessionsMeasurementInput_d5ba7289-9092-474b-9656-9d8a2c1fb37e_terseLabel_en-US" xlink:label="lab_source_RepossessionsMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repossessions unobservable inputs (as a percent)</link:label>
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    <link:label id="lab_source_RepossessionsMeasurementInput_documentation_en-US" xlink:label="lab_source_RepossessionsMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Value of input used to measure repossessions owned by financial institution which is not directly related to its business.</link:label>
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    <link:label id="lab_srt_RegulatoryCapitalRequirementsAbstract_d597a5c6-7415-4703-b82e-6c1dbd531cd0_terseLabel_en-US" xlink:label="lab_srt_RegulatoryCapitalRequirementsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]</link:label>
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    <link:label id="lab_us-gaap_LoansAndLeasesReceivableMortgageBankingActivitiesPolicy_8ee4ed00-9b66-4b5f-8e84-3a6fd761fd9f_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableMortgageBankingActivitiesPolicy" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage Banking Activities</link:label>
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    <link:label id="lab_us-gaap_FinancialAssetNotPastDueMember_86064203-fc45-401c-940d-d926fd2728da_terseLabel_en-US" xlink:label="lab_us-gaap_FinancialAssetNotPastDueMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current</link:label>
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    <link:label id="lab_us-gaap_LongTermDebtByMaturityAbstract_91d9facc-4353-4c9f-b65f-2ee758e78e4b_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtByMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Annual maturities of long-term debt</link:label>
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    <link:label id="lab_us-gaap_LoansAndLeasesReceivableDisclosureAbstract_ff18425c-8394-4bf8-84fe-d3bf3aeb6c1b_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and leases</link:label>
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    <link:label id="lab_dei_EntityEmergingGrowthCompany_b2557568-b57f-46bf-82df-4f7e8e1d3871_terseLabel_en-US" xlink:label="lab_dei_EntityEmergingGrowthCompany" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Emerging Growth Company</link:label>
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    <link:label id="lab_source_ReceivablesMember_documentation_en-US" xlink:label="lab_source_ReceivablesMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Receivables [Member]</link:label>
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    <link:label id="lab_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_cee99c40-c991-4527-adef-a75019c01ee0_terseLabel_en-US" xlink:label="lab_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repurchase Agreements and Similar Transactions, Maturity Periods [Domain]</link:label>
    <link:label id="lab_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain_label_en-US" xlink:label="lab_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repurchase Agreements and Similar Transactions, Maturity Periods [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodDomain"/>
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    <link:label id="lab_source_TaxBenefitRealizedOnSettlementPercentage_05d5a030-f602-4242-bccc-48aea763f58a_terseLabel_en-US" xlink:label="lab_source_TaxBenefitRealizedOnSettlementPercentage" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tax benefit realized on settlement, percentage</link:label>
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    <link:label id="lab_us-gaap_ReceivablesAbstract_6df94b48-0c88-49a6-bcc3-79f5251b9790_terseLabel_en-US" xlink:label="lab_us-gaap_ReceivablesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Receivables [Abstract]</link:label>
    <link:label id="lab_us-gaap_ReceivablesAbstract_label_en-US" xlink:label="lab_us-gaap_ReceivablesAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Receivables [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ReceivablesAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ReceivablesAbstract" xlink:to="lab_us-gaap_ReceivablesAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_OperatingLeaseTerm_db934a85-b787-46cb-a3b5-30c1c35a1425_terseLabel_en-US" xlink:label="lab_source_OperatingLeaseTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease term</link:label>
    <link:label id="lab_source_OperatingLeaseTerm_label_en-US" xlink:label="lab_source_OperatingLeaseTerm" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating Lease Term</link:label>
    <link:label id="lab_source_OperatingLeaseTerm_documentation_en-US" xlink:label="lab_source_OperatingLeaseTerm" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the term of operation leases.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_OperatingLeaseTerm" xlink:href="source-20211231.xsd#source_OperatingLeaseTerm"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_OperatingLeaseTerm" xlink:to="lab_source_OperatingLeaseTerm" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueRollingMaturityAbstract_e6ff222a-a775-42b6-91e8-5592331d37f3_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueRollingMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Contractual maturities of investments in debt securities available-for-sale, Fair Value</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueRollingMaturityAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueRollingMaturityAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueRollingMaturityAbstract" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueRollingMaturityAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_NumberOfTrustsSponsored_5c735e1e-3d48-4fec-a963-a9067cc98b1d_terseLabel_en-US" xlink:label="lab_source_NumberOfTrustsSponsored" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of trusts sponsored</link:label>
    <link:label id="lab_source_NumberOfTrustsSponsored_label_en-US" xlink:label="lab_source_NumberOfTrustsSponsored" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Trusts Sponsored</link:label>
    <link:label id="lab_source_NumberOfTrustsSponsored_documentation_en-US" xlink:label="lab_source_NumberOfTrustsSponsored" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the number of trusts sponsored by the entity.</link:label>
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    <link:label id="lab_dei_AuditorName_462c133c-9b74-4df4-b503-5d065f2c1760_terseLabel_en-US" xlink:label="lab_dei_AuditorName" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auditor Name</link:label>
    <link:label id="lab_dei_AuditorName_label_en-US" xlink:label="lab_dei_AuditorName" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Auditor Name</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AuditorName" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_AuditorName"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_AuditorName" xlink:to="lab_dei_AuditorName" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_CoverAbstract_ba925643-f83e-4fb1-87e8-2b5b803a93b1_terseLabel_en-US" xlink:label="lab_dei_CoverAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cover [Abstract]</link:label>
    <link:label id="lab_dei_CoverAbstract_label_en-US" xlink:label="lab_dei_CoverAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cover [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CoverAbstract" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_CoverAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_CoverAbstract" xlink:to="lab_dei_CoverAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyMinimum_25e82c71-9dd0-4a82-9618-f4f6f8736e33_terseLabel_en-US" xlink:label="lab_us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyMinimum" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy Ratio (as a percent)</link:label>
    <link:label id="lab_us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyMinimum_label_en-US" xlink:label="lab_us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyMinimum" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Capital Adequacy, Minimum</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyMinimum" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BankingRegulationCommonEquityTierOneRiskBasedCapitalRatioCapitalAdequacyMinimum"/>
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    <link:label id="lab_us-gaap_LesseeDisclosureAbstract_1a9e8241-e106-4a37-9f96-e56797ef04d0_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease Commitments</link:label>
    <link:label id="lab_us-gaap_LesseeDisclosureAbstract_label_en-US" xlink:label="lab_us-gaap_LesseeDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee Disclosure [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeDisclosureAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeDisclosureAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeDisclosureAbstract" xlink:to="lab_us-gaap_LesseeDisclosureAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_5376a2f9-f1d9-4c24-8e0a-994ffe2124c2_terseLabel_en-US" xlink:label="lab_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Adjusted Balance</link:label>
    <link:label id="lab_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_label_en-US" xlink:label="lab_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cumulative Effect, Period of Adoption, Adjusted Balance [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember" xlink:to="lab_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_99d82319-adfc-4645-b14a-4afff45b904e_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Credit Quality Indicator [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Credit Quality Indicator [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="lab_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CashAndCashEquivalentsPolicyTextBlock_ec29ac72-026f-4002-a46a-37c90c154bec_terseLabel_en-US" xlink:label="lab_us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash Flows</link:label>
    <link:label id="lab_us-gaap_CashAndCashEquivalentsPolicyTextBlock_label_en-US" xlink:label="lab_us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and Cash Equivalents, Policy [Policy Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsPolicyTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:to="lab_us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TreasuryStockShares_e7721222-3f40-4634-a46c-1eaa5997db65_terseLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockShares" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cost of common stock in treasury, shares</link:label>
    <link:label id="lab_us-gaap_TreasuryStockShares_label_en-US" xlink:label="lab_us-gaap_TreasuryStockShares" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock, Shares</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockShares" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockShares"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TreasuryStockShares" xlink:to="lab_us-gaap_TreasuryStockShares" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock_6686b2bd-533a-41d9-87fd-6c013ab8cad2_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of gross unrealized losses and fair value by investment category and age</link:label>
    <link:label id="lab_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Unrealized Loss on Investments [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock" xlink:to="lab_us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_458fe789-3947-43c0-a659-4890d9e5048e_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Imputed interest</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Liability, Undiscounted Excess Amount</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount"/>
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    <link:label id="lab_us-gaap_PreferredStockNoParValue_b4b3dc28-3881-4e7c-824d-b7980c4d1db4_terseLabel_en-US" xlink:label="lab_us-gaap_PreferredStockNoParValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred Stock, Par or Stated Value Per Share</link:label>
    <link:label id="lab_us-gaap_PreferredStockNoParValue_label_en-US" xlink:label="lab_us-gaap_PreferredStockNoParValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred Stock, No Par Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockNoParValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockNoParValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PreferredStockNoParValue" xlink:to="lab_us-gaap_PreferredStockNoParValue" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock_86723ca8-b9a8-4722-ba22-412cf4190f78_terseLabel_en-US" xlink:label="lab_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of statements of cash flow</link:label>
    <link:label id="lab_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock_label_en-US" xlink:label="lab_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Condensed Cash Flow Statement [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScheduleOfCondensedCashFlowStatementTableTextBlock"/>
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    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRollForward_86bb2469-7a72-4ce5-9f65-0596793c65f8_terseLabel_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Changes in valuation allowance</link:label>
    <link:label id="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRollForward_label_en-US" xlink:label="lab_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRollForward" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Allowance for Impairment of Recognized Servicing Assets [Roll Forward]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRollForward" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRollForward"/>
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    <link:label id="lab_us-gaap_FinancialInstrumentAxis_0b7fd0af-9a9a-46b5-990d-b0c3dcf19bc9_terseLabel_en-US" xlink:label="lab_us-gaap_FinancialInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Instrument [Axis]</link:label>
    <link:label id="lab_us-gaap_FinancialInstrumentAxis_label_en-US" xlink:label="lab_us-gaap_FinancialInstrumentAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Instrument [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancialInstrumentAxis" xlink:to="lab_us-gaap_FinancialInstrumentAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShortTermDebtLineItems_5e91e5d2-f79f-4470-9b4a-8b703046e93b_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermDebtLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term borrowings:</link:label>
    <link:label id="lab_us-gaap_ShortTermDebtLineItems_label_en-US" xlink:label="lab_us-gaap_ShortTermDebtLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShortTermDebtLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShortTermDebtLineItems" xlink:to="lab_us-gaap_ShortTermDebtLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DirectFinanceLeaseTerm_b1557a24-f48e-47e3-9476-75533ea29c3d_terseLabel_en-US" xlink:label="lab_source_DirectFinanceLeaseTerm" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Direct finance lease term</link:label>
    <link:label id="lab_source_DirectFinanceLeaseTerm_label_en-US" xlink:label="lab_source_DirectFinanceLeaseTerm" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">DirectFinanceLeaseTerm</link:label>
    <link:label id="lab_source_DirectFinanceLeaseTerm_documentation_en-US" xlink:label="lab_source_DirectFinanceLeaseTerm" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Direct finance lease term</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DirectFinanceLeaseTerm" xlink:href="source-20211231.xsd#source_DirectFinanceLeaseTerm"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DirectFinanceLeaseTerm" xlink:to="lab_source_DirectFinanceLeaseTerm" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_dabcbc03-1a0a-4159-ac63-1f669a86c8f5_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing receivable originated one year prior to current fiscal year</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear"/>
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    <link:label id="lab_source_MinimumLeaseLiabilityforCapitalization_c0a9fe38-e1e2-40df-ba60-b2353340d33e_terseLabel_en-US" xlink:label="lab_source_MinimumLeaseLiabilityforCapitalization" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum lease liability for capitalization</link:label>
    <link:label id="lab_source_MinimumLeaseLiabilityforCapitalization_label_en-US" xlink:label="lab_source_MinimumLeaseLiabilityforCapitalization" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Lease Liability for Capitalization</link:label>
    <link:label id="lab_source_MinimumLeaseLiabilityforCapitalization_documentation_en-US" xlink:label="lab_source_MinimumLeaseLiabilityforCapitalization" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum amount for lease liability capitalization.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_MinimumLeaseLiabilityforCapitalization" xlink:href="source-20211231.xsd#source_MinimumLeaseLiabilityforCapitalization"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_MinimumLeaseLiabilityforCapitalization" xlink:to="lab_source_MinimumLeaseLiabilityforCapitalization" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract_6da8c69e-26f7-403f-947a-4ebc87492279_terseLabel_en-US" xlink:label="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current:</link:label>
    <link:label id="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract_label_en-US" xlink:label="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Current Income Tax Expense (Benefit), Continuing Operations [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:to="lab_us-gaap_CurrentIncomeTaxExpenseBenefitContinuingOperationsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract_62b3e5b9-4364-44c0-b72b-e31877fdc36f_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating minimum lease payments receivable</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract" xlink:to="lab_us-gaap_LessorOperatingLeasePaymentsFiscalYearMaturityAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember_8be39791-327b-4cd3-8eef-0d83f17ed0ed_verboseLabel_en-US" xlink:label="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Carrying Value</link:label>
    <link:label id="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember_c82bc662-d5e5-4a01-a1e1-a83d6e90da52_terseLabel_en-US" xlink:label="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Carrying or Contract Value</link:label>
    <link:label id="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember_label_en-US" xlink:label="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Reported Value Measurement [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:to="lab_us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PaymentsForProceedsFromLoansAndLeases_dc300c61-be9a-49b1-817b-68a79f5e31f4_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in loans and leases</link:label>
    <link:label id="lab_us-gaap_PaymentsForProceedsFromLoansAndLeases_label_en-US" xlink:label="lab_us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments for (Proceeds from) Loans and Leases</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForProceedsFromLoansAndLeases"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:to="lab_us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommonStockMember_b8e01398-2194-429a-9ab6-7f4f76a77d45_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Stock</link:label>
    <link:label id="lab_us-gaap_CommonStockMember_label_en-US" xlink:label="lab_us-gaap_CommonStockMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Stock [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommonStockMember" xlink:to="lab_us-gaap_CommonStockMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract_d4cc8392-586f-4a48-bce1-cbb89abad448_terseLabel_en-US" xlink:label="lab_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfers and Servicing of Financial Assets [Abstract]</link:label>
    <link:label id="lab_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract_label_en-US" xlink:label="lab_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfers and Servicing of Financial Assets [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialAssetsAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract" xlink:to="lab_us-gaap_TransfersAndServicingOfFinancialAssetsAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription_bf83507a-432b-42c8-8131-3eaf2cd790a5_terseLabel_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Residual value guarantees or restriction or covenants imposed by leases</link:label>
    <link:label id="lab_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription_label_en-US" xlink:label="lab_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessee, Operating Lease, Residual Value Guarantee, Description</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription" xlink:to="lab_us-gaap_LesseeOperatingLeaseResidualValueGuaranteeDescription" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_FinancingReceivableModificationsNumberOfContracts2_30ccea97-a23f-4854-9984-bab4e583a9ad_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Modifications, Number of Contracts</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableModificationsNumberOfContracts2_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Modifications, Number of Contracts</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:to="lab_us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CashPaidForAbstract_dfe17b7d-83b9-4b61-8659-715d574f5a24_terseLabel_en-US" xlink:label="lab_source_CashPaidForAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash paid for:</link:label>
    <link:label id="lab_source_CashPaidForAbstract_label_en-US" xlink:label="lab_source_CashPaidForAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash Paid for [Abstract]</link:label>
    <link:label id="lab_source_CashPaidForAbstract_documentation_en-US" xlink:label="lab_source_CashPaidForAbstract" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CashPaidForAbstract" xlink:href="source-20211231.xsd#source_CashPaidForAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CashPaidForAbstract" xlink:to="lab_source_CashPaidForAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AssetImpairmentCharges_b03cf53a-8312-4d9d-aa65-04f673475a62_terseLabel_en-US" xlink:label="lab_us-gaap_AssetImpairmentCharges" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Impairment charges</link:label>
    <link:label id="lab_us-gaap_AssetImpairmentCharges_label_en-US" xlink:label="lab_us-gaap_AssetImpairmentCharges" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Asset Impairment Charges</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AssetImpairmentCharges" xlink:to="lab_us-gaap_AssetImpairmentCharges" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeNotionalAmount_2e547de2-93ef-41ec-8a0b-07f80d31e9ff_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeNotionalAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative, Notional Amount</link:label>
    <link:label id="lab_us-gaap_DerivativeNotionalAmount_label_en-US" xlink:label="lab_us-gaap_DerivativeNotionalAmount" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative, Notional Amount</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeNotionalAmount" xlink:to="lab_us-gaap_DerivativeNotionalAmount" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock_77dd322c-321f-4a4a-bda7-596f518fc156_terseLabel_en-US" xlink:label="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of the components of income from direct finance and operating lease equipment</link:label>
    <link:label id="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock_label_en-US" xlink:label="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of the Components of Income from Direct Finance and Operating Lease Equipment [Table Text Block]</link:label>
    <link:label id="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock_documentation_en-US" xlink:label="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">[Table Text Block] for Tabular disclosure of the components of income from direct finance and operating lease equipment.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock" xlink:href="source-20211231.xsd#source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock" xlink:to="lab_source_ScheduleoftheComponentsofIncomefromDirectFinanceandOperatingLeaseEquipmentTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StockIssued1_7b4c000a-34d5-497b-b30a-33f76a2e05b3_terseLabel_en-US" xlink:label="lab_us-gaap_StockIssued1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock matching contribution to Employee Stock Ownership and Profit Sharing Plan</link:label>
    <link:label id="lab_us-gaap_StockIssued1_label_en-US" xlink:label="lab_us-gaap_StockIssued1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock Issued</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssued1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssued1"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StockIssued1" xlink:to="lab_us-gaap_StockIssued1" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization_6e4fe95a-d981-46c5-ad96-3876cf0d62eb_terseLabel_en-US" xlink:label="lab_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Aggregate unpaid principal</link:label>
    <link:label id="lab_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization_label_en-US" xlink:label="lab_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Principal Amount Outstanding on Loans Held-for-sale or Securitization or Asset-backed Financing Arrangement</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization" xlink:to="lab_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_2278bbf2-effc-42b2-9be7-fc8e2db8aeed_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Purchases of premises and equipment</link:label>
    <link:label id="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_label_en-US" xlink:label="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Payments to Acquire Property, Plant, and Equipment</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:to="lab_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ValuationTechniqueAxis_82c53b51-89f6-48ec-91e0-ada10990d110_terseLabel_en-US" xlink:label="lab_us-gaap_ValuationTechniqueAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Approach and Technique [Axis]</link:label>
    <link:label id="lab_us-gaap_ValuationTechniqueAxis_label_en-US" xlink:label="lab_us-gaap_ValuationTechniqueAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation Approach and Technique [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ValuationTechniqueAxis" xlink:to="lab_us-gaap_ValuationTechniqueAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_Liabilities_ae411f6b-48a9-4a75-97aa-6c6083e04c33_totalLabel_en-US" xlink:label="lab_us-gaap_Liabilities" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total liabilities</link:label>
    <link:label id="lab_us-gaap_Liabilities_32a18675-ec49-4ed7-8587-03479a3f1dae_terseLabel_en-US" xlink:label="lab_us-gaap_Liabilities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unfunded capital and other commitments</link:label>
    <link:label id="lab_us-gaap_Liabilities_label_en-US" xlink:label="lab_us-gaap_Liabilities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liabilities</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Liabilities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Liabilities" xlink:to="lab_us-gaap_Liabilities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InternalCreditAssessmentAxis_7b1407df-63d3-4452-8bdc-8a5c686d1036_terseLabel_en-US" xlink:label="lab_us-gaap_InternalCreditAssessmentAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Internal Credit Assessment [Axis]</link:label>
    <link:label id="lab_us-gaap_InternalCreditAssessmentAxis_label_en-US" xlink:label="lab_us-gaap_InternalCreditAssessmentAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Internal Credit Assessment [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InternalCreditAssessmentAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis" xlink:to="lab_us-gaap_InternalCreditAssessmentAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus_ce3e4ff5-b661-4069-806b-08c5ecae4399_terseLabel_en-US" xlink:label="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Period of sustained performance required to change from non-performing to performing status</link:label>
    <link:label id="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus_label_en-US" xlink:label="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Sustained Performance Period Required for Performing Status</link:label>
    <link:label id="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus_documentation_en-US" xlink:label="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the period of sustained performance required to change loan from non-performing to performing.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_SustainedPerformancePeriodRequiredForPerformingStatus" xlink:href="source-20211231.xsd#source_SustainedPerformancePeriodRequiredForPerformingStatus"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_SustainedPerformancePeriodRequiredForPerformingStatus" xlink:to="lab_source_SustainedPerformancePeriodRequiredForPerformingStatus" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_3249e071-f518-43dc-9ea2-2390c5064e99_terseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2022</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_label_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Asset, Expected Amortization, Year One</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:to="lab_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MeasurementInputTypeAxis_5b8ecce2-392c-45c5-8bf4-1cf1b98a104c_terseLabel_en-US" xlink:label="lab_us-gaap_MeasurementInputTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Input Type [Axis]</link:label>
    <link:label id="lab_us-gaap_MeasurementInputTypeAxis_label_en-US" xlink:label="lab_us-gaap_MeasurementInputTypeAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Input Type [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MeasurementInputTypeAxis" xlink:to="lab_us-gaap_MeasurementInputTypeAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CommonStockSharesIssued_ce661aa9-7333-4e06-9619-63bf57e5cc36_terseLabel_en-US" xlink:label="lab_us-gaap_CommonStockSharesIssued" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock, issued shares</link:label>
    <link:label id="lab_us-gaap_CommonStockSharesIssued_label_en-US" xlink:label="lab_us-gaap_CommonStockSharesIssued" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Stock, Shares, Issued</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommonStockSharesIssued" xlink:to="lab_us-gaap_CommonStockSharesIssued" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue_2aee1b67-ad84-4b35-b395-302f341ca48c_terseLabel_en-US" xlink:label="lab_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral security</link:label>
    <link:label id="lab_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue_label_en-US" xlink:label="lab_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Security Owned and Pledged as Collateral, Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue" xlink:to="lab_us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PreferredStockSharesIssued_7f3873ae-7a13-47c1-82f2-94e85313a814_terseLabel_en-US" xlink:label="lab_us-gaap_PreferredStockSharesIssued" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred stock, issued shares</link:label>
    <link:label id="lab_us-gaap_PreferredStockSharesIssued_label_en-US" xlink:label="lab_us-gaap_PreferredStockSharesIssued" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Preferred Stock, Shares Issued</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PreferredStockSharesIssued" xlink:to="lab_us-gaap_PreferredStockSharesIssued" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestExpenseTrustPreferredSecurities_4803e5ac-97a3-4732-bb32-9a61efaa0ca7_terseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseTrustPreferredSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated notes</link:label>
    <link:label id="lab_us-gaap_InterestExpenseTrustPreferredSecurities_9ad4ed2f-492a-4546-949f-c7fcb4975f77_verboseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseTrustPreferredSecurities" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest on subordinated notes</link:label>
    <link:label id="lab_us-gaap_InterestExpenseTrustPreferredSecurities_label_en-US" xlink:label="lab_us-gaap_InterestExpenseTrustPreferredSecurities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Expense, Trust Preferred Securities</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseTrustPreferredSecurities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseTrustPreferredSecurities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestExpenseTrustPreferredSecurities" xlink:to="lab_us-gaap_InterestExpenseTrustPreferredSecurities" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer_ecf4bf5d-0c5a-4ece-8586-a2013a7acdf1_terseLabel_en-US" xlink:label="lab_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy with Capital Buffer Amount</link:label>
    <link:label id="lab_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer_label_en-US" xlink:label="lab_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common Equity Tier 1 Capita Required Form Minimum Capital Adequacy With Capital Buffer</link:label>
    <link:label id="lab_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer_documentation_en-US" xlink:label="lab_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The minimum amount of Common Equity Tier 1 Capital required for capital adequacy with capital buffer purposes under the regulatory framework for prompt corrective action.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer" xlink:href="source-20211231.xsd#source_CommonEquityTier1CapitaRequiredFormMinimumCapitalAdequacyWithCapitalBuffer"/>
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    <link:label id="lab_dei_EntityAddressCityOrTown_00500af4-66db-42ac-bfec-6b937371c9ce_terseLabel_en-US" xlink:label="lab_dei_EntityAddressCityOrTown" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, City or Town</link:label>
    <link:label id="lab_dei_EntityAddressCityOrTown_label_en-US" xlink:label="lab_dei_EntityAddressCityOrTown" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Address, City or Town</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityAddressCityOrTown"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityAddressCityOrTown" xlink:to="lab_dei_EntityAddressCityOrTown" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LessorOperatingLeaseDescriptionAbstract_f718fb68-d84f-4e25-99d5-53c8fb6d45ff_terseLabel_en-US" xlink:label="lab_us-gaap_LessorOperatingLeaseDescriptionAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equipment owned under operating lease</link:label>
    <link:label id="lab_us-gaap_LessorOperatingLeaseDescriptionAbstract_label_en-US" xlink:label="lab_us-gaap_LessorOperatingLeaseDescriptionAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lessor, Operating Lease, Description [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseDescriptionAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LessorOperatingLeaseDescriptionAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LessorOperatingLeaseDescriptionAbstract" xlink:to="lab_us-gaap_LessorOperatingLeaseDescriptionAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan_ce19bbc6-535c-4c6c-9a0d-ebf0629debfe_terseLabel_en-US" xlink:label="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Percentage of the principal balance that may be repurchased of a delinquent Ginnie Mae (GNMA) mortgage loan (as a percent)</link:label>
    <link:label id="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan_label_en-US" xlink:label="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Percentage of Principal Balance that May be Repurchased of Delinquent Mortgage Loan</link:label>
    <link:label id="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan_documentation_en-US" xlink:label="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the percentage of the principal balance that may be repurchased of a delinquent Ginnie Mae (GNMA) mortgage loan.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan" xlink:href="source-20211231.xsd#source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan" xlink:to="lab_source_PercentageOfPrincipalBalanceThatMayBeRepurchasedOfDelinquentMortgageLoan" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromSaleOfForeclosedAssets_251ad300-119d-4669-9d4e-1450b7af3517_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from sales of other real estate and repossessions</link:label>
    <link:label id="lab_us-gaap_ProceedsFromSaleOfForeclosedAssets_label_en-US" xlink:label="lab_us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from Sale of Foreclosed Assets</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleOfForeclosedAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:to="lab_us-gaap_ProceedsFromSaleOfForeclosedAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_e22e093c-9772-48dc-9ce4-393877bf8b85_negatedLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross realized losses</link:label>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_label_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Realized Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss" xlink:to="lab_us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ResidentialMortgageMember_486c473d-a37e-492e-b2c6-79a908a5bbf2_terseLabel_en-US" xlink:label="lab_us-gaap_ResidentialMortgageMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Residential mortgage loans</link:label>
    <link:label id="lab_us-gaap_ResidentialMortgageMember_label_en-US" xlink:label="lab_us-gaap_ResidentialMortgageMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Residential Mortgage [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialMortgageMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResidentialMortgageMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ResidentialMortgageMember" xlink:to="lab_us-gaap_ResidentialMortgageMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PerformingFinancingReceivableMember_66f7062a-9d57-4b3c-89de-f6c47eb99b3f_terseLabel_en-US" xlink:label="lab_us-gaap_PerformingFinancingReceivableMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Performing</link:label>
    <link:label id="lab_us-gaap_PerformingFinancingReceivableMember_label_en-US" xlink:label="lab_us-gaap_PerformingFinancingReceivableMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Performing Financial Instruments [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformingFinancingReceivableMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformingFinancingReceivableMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PerformingFinancingReceivableMember" xlink:to="lab_us-gaap_PerformingFinancingReceivableMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_NonvestedStockAwardsOrUnitsMember_fabe8eac-6789-4f10-9a47-ea08bba9209b_terseLabel_en-US" xlink:label="lab_source_NonvestedStockAwardsOrUnitsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Non-vested stock awards outstanding</link:label>
    <link:label id="lab_source_NonvestedStockAwardsOrUnitsMember_label_en-US" xlink:label="lab_source_NonvestedStockAwardsOrUnitsMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Nonvested Stock Awards or Units [Member]</link:label>
    <link:label id="lab_source_NonvestedStockAwardsOrUnitsMember_documentation_en-US" xlink:label="lab_source_NonvestedStockAwardsOrUnitsMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents nonvested stock awards or units used to compensate employees.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_NonvestedStockAwardsOrUnitsMember" xlink:href="source-20211231.xsd#source_NonvestedStockAwardsOrUnitsMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_NonvestedStockAwardsOrUnitsMember" xlink:to="lab_source_NonvestedStockAwardsOrUnitsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ComprehensiveIncomeNoteTextBlock_24924840-8e25-4eac-85fc-7c73e1dabe51_terseLabel_en-US" xlink:label="lab_us-gaap_ComprehensiveIncomeNoteTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Other Comprehensive Income</link:label>
    <link:label id="lab_us-gaap_ComprehensiveIncomeNoteTextBlock_label_en-US" xlink:label="lab_us-gaap_ComprehensiveIncomeNoteTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Comprehensive Income (Loss) Note [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNoteTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComprehensiveIncomeNoteTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ComprehensiveIncomeNoteTextBlock" xlink:to="lab_us-gaap_ComprehensiveIncomeNoteTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfShortTermDebtTable_dde1f2f4-7ed6-4b3c-9e6b-50bd9c1ae20b_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfShortTermDebtTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Short-term Debt [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfShortTermDebtTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfShortTermDebtTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Short-term Debt [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShortTermDebtTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShortTermDebtTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfShortTermDebtTable" xlink:to="lab_us-gaap_ScheduleOfShortTermDebtTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueMeasurementFrequencyDomain_164dd38d-5ceb-4a11-b04b-1b92eb437f2b_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementFrequencyDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Frequency [Domain]</link:label>
    <link:label id="lab_us-gaap_FairValueMeasurementFrequencyDomain_label_en-US" xlink:label="lab_us-gaap_FairValueMeasurementFrequencyDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Measurement Frequency [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="lab_us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LoanRestructuringModificationDomain_18af941f-45ca-4523-b214-9c8a597f0c67_terseLabel_en-US" xlink:label="lab_us-gaap_LoanRestructuringModificationDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan Restructuring Modification [Domain]</link:label>
    <link:label id="lab_us-gaap_LoanRestructuringModificationDomain_label_en-US" xlink:label="lab_us-gaap_LoanRestructuringModificationDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loan Restructuring Modification [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain" xlink:to="lab_us-gaap_LoanRestructuringModificationDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestExpense_ff9af2ee-d91a-457c-9826-aaba0246eaa5_totalLabel_en-US" xlink:label="lab_us-gaap_InterestExpense" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total interest expense</link:label>
    <link:label id="lab_us-gaap_InterestExpense_label_en-US" xlink:label="lab_us-gaap_InterestExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Expense</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpense"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestExpense" xlink:to="lab_us-gaap_InterestExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShortTermDebtWeightedAverageInterestRate_63419260-87d4-4fb4-85ae-73cc2a679b30_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term borrowings, weighted average interest rate</link:label>
    <link:label id="lab_us-gaap_ShortTermDebtWeightedAverageInterestRate_label_en-US" xlink:label="lab_us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term Debt, Weighted Average Interest Rate, at Point in Time</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShortTermDebtWeightedAverageInterestRate"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:to="lab_us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:type="arc" order="1"/>
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    <link:label id="lab_us-gaap_InterestAndDividendIncomeOperating_f4131579-28e3-4e03-a29c-fac2ba468275_totalLabel_en-US" xlink:label="lab_us-gaap_InterestAndDividendIncomeOperating" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total interest income</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:to="lab_us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_OtherShortTermDebtMember_22c28106-5367-4b11-b7d3-e0f1f0d19f99_terseLabel_en-US" xlink:label="lab_source_OtherShortTermDebtMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other short-term borrowings</link:label>
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    <link:label id="lab_source_OtherShortTermDebtMember_documentation_en-US" xlink:label="lab_source_OtherShortTermDebtMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to other short-term debt which is not elsewhere specified.</link:label>
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    <link:label id="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense_dd4b1a02-ff9b-42ba-b0cd-794318669199_terseLabel_en-US" xlink:label="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">FDIC and other insurance</link:label>
    <link:label id="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense_label_en-US" xlink:label="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal Deposit Insurance Corporation Premium and Other Insurance Expense</link:label>
    <link:label id="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense_documentation_en-US" xlink:label="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">This element represents the premium paid to the Federal Deposit Insurance Corporation for deposit insurance which is included in noninterest expense. Also includes other insurance expenses.</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense" xlink:to="lab_source_FederalDepositInsuranceCorporationPremiumAndOtherInsuranceExpense" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DeferredCompensationArrangementWithIndividualsRequisiteServicePeriod_83e4ef73-b4a5-4d3f-aeec-c19b0511ccdb_terseLabel_en-US" xlink:label="lab_source_DeferredCompensationArrangementWithIndividualsRequisiteServicePeriod" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum service period required to be eligible to get employer's contribution</link:label>
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    <link:label id="lab_source_DeferredCompensationArrangementWithIndividualsRequisiteServicePeriod_documentation_en-US" xlink:label="lab_source_DeferredCompensationArrangementWithIndividualsRequisiteServicePeriod" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The minimum credited years of service that an individual is required to perform in order to be fully vested under the deferred compensation arrangement.</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DeferredCompensationArrangementWithIndividualsRequisiteServicePeriod" xlink:to="lab_source_DeferredCompensationArrangementWithIndividualsRequisiteServicePeriod" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_RetainedEarningsAccumulatedDeficit_63df6cb3-6fc0-4e6b-88ef-c4d9c8f6bccb_terseLabel_en-US" xlink:label="lab_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retained earnings</link:label>
    <link:label id="lab_us-gaap_RetainedEarningsAccumulatedDeficit_label_en-US" xlink:label="lab_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Retained Earnings (Accumulated Deficit)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="lab_us-gaap_RetainedEarningsAccumulatedDeficit" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_ccee957c-ccf3-409f-a16b-51af5914bd92_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Measurement Inputs and Valuation Techniques [Table]</link:label>
    <link:label id="lab_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_label_en-US" xlink:label="lab_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value Measurement Inputs and Valuation Techniques [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="lab_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_3be419d3-3afe-40e3-8744-1c83a1502fca_terseLabel_en-US" xlink:label="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recoveries</link:label>
    <link:label id="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_label_en-US" xlink:label="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Allowance for Credit Loss, Recovery</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:to="lab_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StatementOfStockholdersEquityAbstract_75b5056c-8480-48c8-9d42-4db1141d6a10_terseLabel_en-US" xlink:label="lab_us-gaap_StatementOfStockholdersEquityAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Stockholders' Equity [Abstract]</link:label>
    <link:label id="lab_us-gaap_StatementOfStockholdersEquityAbstract_label_en-US" xlink:label="lab_us-gaap_StatementOfStockholdersEquityAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Stockholders' Equity [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfStockholdersEquityAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementOfStockholdersEquityAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementOfStockholdersEquityAbstract" xlink:to="lab_us-gaap_StatementOfStockholdersEquityAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityFilerCategory_8c7c681b-638d-47fe-a69c-57c11126c6a8_terseLabel_en-US" xlink:label="lab_dei_EntityFilerCategory" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Filer Category</link:label>
    <link:label id="lab_dei_EntityFilerCategory_label_en-US" xlink:label="lab_dei_EntityFilerCategory" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Filer Category</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityFilerCategory"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityFilerCategory" xlink:to="lab_dei_EntityFilerCategory" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_GainLossOnInvestments_8e5f1c8f-1181-4a81-8fdf-3ed3a41834eb_verboseLabel_en-US" xlink:label="lab_us-gaap_GainLossOnInvestments" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment securities and other investment gains (losses)</link:label>
    <link:label id="lab_us-gaap_GainLossOnInvestments_e7f0dcdb-725a-4fec-b3df-bd7962a7f3e3_negatedTerseLabel_en-US" xlink:label="lab_us-gaap_GainLossOnInvestments" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Realized/unrealized investment securities and other investment (gains) losses</link:label>
    <link:label id="lab_us-gaap_GainLossOnInvestments_label_en-US" xlink:label="lab_us-gaap_GainLossOnInvestments" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gain (Loss) on Investments</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnInvestments"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_GainLossOnInvestments" xlink:to="lab_us-gaap_GainLossOnInvestments" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_92c46c8e-39ff-4eae-b6be-eaf13ec7a3d3_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of amounts included in the consolidated statements of income for non-hedging derivative financial instruments</link:label>
    <link:label id="lab_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Instruments, Gain (Loss) [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock" xlink:to="lab_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_InterestRateBelowMarketReductionMember_94026ac5-ae95-4e52-83ef-94cda39fe66c_terseLabel_en-US" xlink:label="lab_us-gaap_InterestRateBelowMarketReductionMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Rate Below Market Reduction</link:label>
    <link:label id="lab_us-gaap_InterestRateBelowMarketReductionMember_label_en-US" xlink:label="lab_us-gaap_InterestRateBelowMarketReductionMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Interest Rate Below Market Reduction [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateBelowMarketReductionMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestRateBelowMarketReductionMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_InterestRateBelowMarketReductionMember" xlink:to="lab_us-gaap_InterestRateBelowMarketReductionMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember_99f07655-06fa-4ba1-bbbc-e96124599574_terseLabel_en-US" xlink:label="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total</link:label>
    <link:label id="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember_661e9f93-7dfe-4bbf-ae08-82132e4924e6_verboseLabel_en-US" xlink:label="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value</link:label>
    <link:label id="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember_label_en-US" xlink:label="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Estimate of Fair Value Measurement [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:to="lab_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:type="arc" order="1"/>
    <link:label id="lab_source_EquityMethodInvestmentOwnershipPercentageMaximum_37335efc-de78-4dd2-92a5-608caea85546_terseLabel_en-US" xlink:label="lab_source_EquityMethodInvestmentOwnershipPercentageMaximum" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maximum percentage of partnership accounted for as equity investment</link:label>
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    <link:label id="lab_us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_58879265-0a07-406f-8f1b-45fe4a3bf0e9_terseLabel_en-US" xlink:label="lab_us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Recent Accounting Pronouncements</link:label>
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    <link:label id="lab_us-gaap_ShortTermInvestments_a24d7721-c9f3-4d6e-81b3-cd93cc14fa93_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermInvestments" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term investments with bank subsidiary</link:label>
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    <link:label id="lab_us-gaap_DerivativeAssetFairValueAmountOffsetAgainstCollateralAbstract_017acdc0-2471-4092-8d09-7a9c377a3a64_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeAssetFairValueAmountOffsetAgainstCollateralAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Amounts Not Offset in the Statement of Financial Condition</link:label>
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    <link:label id="lab_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_4cb3736a-e1fa-45f2-99c5-a63f324c43c6_totalLabel_en-US" xlink:label="lab_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total equity</link:label>
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    <link:label id="lab_source_RepossessedAssetsPolicyTextBlock_cb00ac9d-8d52-4a56-99eb-7ceb533b05db_terseLabel_en-US" xlink:label="lab_source_RepossessedAssetsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repossessed Assets</link:label>
    <link:label id="lab_source_RepossessedAssetsPolicyTextBlock_label_en-US" xlink:label="lab_source_RepossessedAssetsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Repossessed Assets [Policy Text Block]</link:label>
    <link:label id="lab_source_RepossessedAssetsPolicyTextBlock_documentation_en-US" xlink:label="lab_source_RepossessedAssetsPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Disclosure of accounting policy for repossessed assets.</link:label>
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    <link:label id="lab_dei_AmendmentFlag_c426146e-a33a-4639-8b63-97cfe3d1efb6_terseLabel_en-US" xlink:label="lab_dei_AmendmentFlag" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amendment Flag</link:label>
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    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionAmount_13ffb9cf-4763-4dc7-8d9f-6c48e5235cc3_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Maximum stock which can be purchased by employee per year</link:label>
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    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionAmount_documentation_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionAmount" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the maximum amount of annual salary that an employee is permitted to utilize with respect to the plan.</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionAmount" xlink:to="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionAmount" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromIssuanceOfLongTermDebt_4910e15b-242c-4cc4-9a02-07deda0639f2_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from issuance of long-term debt</link:label>
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    <link:label id="lab_us-gaap_AmortizationOfMortgageServicingRightsMSRs_4e548495-790f-48b3-b330-b7fde1aa442e_terseLabel_en-US" xlink:label="lab_us-gaap_AmortizationOfMortgageServicingRightsMSRs" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amortization of mortgage servicing rights</link:label>
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    <link:label id="lab_us-gaap_StatementEquityComponentsAxis_3792d3d4-b751-47a4-a998-7d441a3c1620_terseLabel_en-US" xlink:label="lab_us-gaap_StatementEquityComponentsAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equity Components [Axis]</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementEquityComponentsAxis" xlink:to="lab_us-gaap_StatementEquityComponentsAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentExcludingLessorAssetUnderOperatingLeaseAfterAccumulatedDepreciation_cf037b37-7dab-4548-a693-85a85921f797_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentExcludingLessorAssetUnderOperatingLeaseAfterAccumulatedDepreciation" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net premises and equipment</link:label>
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    <link:label id="lab_us-gaap_LoansAndLeasesReceivableNetReportedAmount_4162112c-964a-44ba-b0de-5619196dfe08_totalLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net loans and leases</link:label>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableNetReportedAmount_efbbfb11-0b28-4473-878c-9065111ea80a_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and leases, net of reserve for loan and lease losses</link:label>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableNetReportedAmount_label_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases Receivable, Net Amount</link:label>
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    <link:label id="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesDisclosureAbstract_2037b8e3-5f01-4a42-8a5a-d18f9ee0b88a_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableRelatedPartiesDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans to certain directors, executive officers, and principal shareholders of equity securities of the entity and to their affiliates</link:label>
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    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtSecurities_39eba5dc-a309-490f-85d7-c35ad7390ce9_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment securities available-for-sale</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesDebtSecurities_0afc4618-6c0f-43de-829f-da2c9504f5bc_totalLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total debt securities available-for-sale</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
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    <link:label id="lab_us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale_e87bf3a8-041b-4ea7-8695-6ec64a2496b9_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Originations of loans held for sale, net of principal collected</link:label>
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    <link:label id="lab_us-gaap_DebtDisclosureAbstract_9f402cdf-8cec-478d-b44d-8975f81cebf8_terseLabel_en-US" xlink:label="lab_us-gaap_DebtDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Disclosure [Abstract]</link:label>
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    <link:label id="lab_us-gaap_NoninterestExpenseAbstract_358ad3e5-8a8f-4c2e-b018-65394794190c_terseLabel_en-US" xlink:label="lab_us-gaap_NoninterestExpenseAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noninterest expense:</link:label>
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b3dbc704-c8e6-4bcb-9598-e6ddb8f6e6c1_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment, Type [Axis]</link:label>
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    <link:label id="lab_us-gaap_DeferredTaxAssetsValuationAllowance_a1830951-0134-41f4-98a6-79e62b5e904c_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxAssetsValuationAllowance" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Valuation allowance for deferred tax assets</link:label>
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    <link:label id="lab_us-gaap_TierOneLeverageCapitalAbstract_8f5b26d3-6a40-441e-a07a-ab3e2d0b4a22_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tier I Capital (to Average Assets):</link:label>
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    <link:label id="lab_us-gaap_OtherExpenseMember_1d167fa5-19b8-44ec-a46f-9c9824765fef_terseLabel_en-US" xlink:label="lab_us-gaap_OtherExpenseMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other expense</link:label>
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    <link:label id="lab_us-gaap_InterestExpenseShortTermBorrowings_df4c5da0-72d2-46e8-95b4-e4f3cc98ca37_terseLabel_en-US" xlink:label="lab_us-gaap_InterestExpenseShortTermBorrowings" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Short-term borrowings</link:label>
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    <link:label id="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_08c05f1c-0e81-4de6-9759-f1f75c401a49_terseLabel_en-US" xlink:label="lab_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employee Benefit Plans</link:label>
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    <link:label id="lab_us-gaap_InsuranceCommissionsAndFees_6a814111-2eb8-4521-8fcb-f0e7fe8ddd3d_terseLabel_en-US" xlink:label="lab_us-gaap_InsuranceCommissionsAndFees" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Insurance commissions</link:label>
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    <link:label id="lab_us-gaap_FairValueByAssetClassAxis_2340e03d-1865-414e-ae25-dd7dd705ebbf_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueByAssetClassAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Asset Class [Axis]</link:label>
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    <link:label id="lab_us-gaap_ResidualValueOfLeasedAsset_47747596-08bc-44cd-ab40-7ee37b432bcc_terseLabel_en-US" xlink:label="lab_us-gaap_ResidualValueOfLeasedAsset" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Carrying amount of residual assets covered by residual value guarantees</link:label>
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    <link:label id="lab_us-gaap_NoncontrollingInterestMember_label_en-US" xlink:label="lab_us-gaap_NoncontrollingInterestMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Noncontrolling Interest [Member]</link:label>
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    <link:label id="lab_us-gaap_DerivativeContractTypeDomain_2d1ff0b1-be65-4fbc-ada5-1d8bf34e99f2_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeContractTypeDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Contract Type [Domain]</link:label>
    <link:label id="lab_us-gaap_DerivativeContractTypeDomain_label_en-US" xlink:label="lab_us-gaap_DerivativeContractTypeDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Contract [Domain]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs"/>
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    <link:label id="lab_source_LesseeOperatingLeaseRightofUseAssetsandLiabilitiesTableTextBlock_49472581-e9f2-4a76-a181-e303f45af5ca_terseLabel_en-US" xlink:label="lab_source_LesseeOperatingLeaseRightofUseAssetsandLiabilitiesTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating lease right of use assets and operating lease liabilities</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_b73e170e-190f-4d19-94ba-51e312a8ecad_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in operating activities</link:label>
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    <link:label id="lab_us-gaap_ShortTermBorrowings_d2ebaf86-6ae2-4c1e-b36f-061c1d349f32_totalLabel_en-US" xlink:label="lab_us-gaap_ShortTermBorrowings" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total short-term borrowings</link:label>
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    <link:label id="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesAvailableForGrantRollForward_edff21a3-fc98-487f-8405-d425349a2bd1_terseLabel_en-US" xlink:label="lab_source_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesAvailableForGrantRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Shares Available for Grant</link:label>
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    <link:label id="lab_us-gaap_FurnitureAndFixturesMember_b03b1de1-6b99-4c33-a6da-ffb61a1d6679_terseLabel_en-US" xlink:label="lab_us-gaap_FurnitureAndFixturesMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Furniture and equipment</link:label>
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    <link:label id="lab_us-gaap_MarketableSecuritiesAbstract_76c7f726-4e5e-4bb6-950c-6c2a8e5a48bf_terseLabel_en-US" xlink:label="lab_us-gaap_MarketableSecuritiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Securities</link:label>
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    <link:label id="lab_us-gaap_FederalHomeLoanBankBorrowingsMember_9b655251-23b0-4ae7-aba9-1aaf4576fa75_terseLabel_en-US" xlink:label="lab_us-gaap_FederalHomeLoanBankBorrowingsMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal Home Loan Bank borrowings</link:label>
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    <link:label id="lab_us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_3e305c90-0831-4b84-8600-0d646a591a4a_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of reasons for the difference between income tax expense and the amount computed by applying the statutory federal income tax rate</link:label>
    <link:label id="lab_us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]</link:label>
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    <link:label id="lab_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_ff24afdf-682f-441f-aeb0-9382bdc07b6d_terseLabel_en-US" xlink:label="lab_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable interest entity, primary beneficiary</link:label>
    <link:label id="lab_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_label_en-US" xlink:label="lab_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Variable Interest Entity, Primary Beneficiary [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember" xlink:to="lab_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ParentMember_9cb8fa3b-5d42-47f1-b6a3-6761a02cc814_terseLabel_en-US" xlink:label="lab_us-gaap_ParentMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total Shareholders' Equity</link:label>
    <link:label id="lab_us-gaap_ParentMember_label_en-US" xlink:label="lab_us-gaap_ParentMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Parent [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ParentMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ParentMember" xlink:to="lab_us-gaap_ParentMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CollateralAxis_657662cc-8246-4bbf-9444-836a1df8aff5_terseLabel_en-US" xlink:label="lab_us-gaap_CollateralAxis" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral [Axis]</link:label>
    <link:label id="lab_us-gaap_CollateralAxis_label_en-US" xlink:label="lab_us-gaap_CollateralAxis" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Collateral Held [Axis]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralAxis" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CollateralAxis"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CollateralAxis" xlink:to="lab_us-gaap_CollateralAxis" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract_b367ff3b-2dc5-4472-918d-d77eb971cedd_terseLabel_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and leases, net of unearned discount:</link:label>
    <link:label id="lab_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract_label_en-US" xlink:label="lab_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Loans and Leases Receivable, Net of Deferred Income [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract" xlink:to="lab_us-gaap_LoansAndLeasesReceivableNetOfDeferredIncomeAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_2dd2fb71-b99d-44c5-b816-5d4ad787cb42_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of assets and liabilities measured at fair value on a recurring basis</link:label>
    <link:label id="lab_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:to="lab_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfVariableInterestEntitiesTextBlock_94c9498e-0097-42c4-95b1-f5f715699b73_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfVariableInterestEntitiesTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of unconsolidated variable interest entities</link:label>
    <link:label id="lab_us-gaap_ScheduleOfVariableInterestEntitiesTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfVariableInterestEntitiesTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Variable Interest Entities [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTextBlock"/>
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    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeMember_0a77c8c8-b14f-4a30-bd37-76f2f680e270_terseLabel_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accumulated Other Comprehensive Income (Loss), Net</link:label>
    <link:label id="lab_us-gaap_AccumulatedOtherComprehensiveIncomeMember_label_en-US" xlink:label="lab_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">AOCI Attributable to Parent [Member]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:to="lab_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherAssets_de1d560c-8408-42d9-8394-b427d7bdd700_terseLabel_en-US" xlink:label="lab_us-gaap_OtherAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued income and other assets</link:label>
    <link:label id="lab_us-gaap_OtherAssets_b4026ae8-d974-4c7a-8803-e4d346765240_verboseLabel_en-US" xlink:label="lab_us-gaap_OtherAssets" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other assets</link:label>
    <link:label id="lab_us-gaap_OtherAssets_label_en-US" xlink:label="lab_us-gaap_OtherAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Assets</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherAssets" xlink:to="lab_us-gaap_OtherAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueAdditions_fbbacd88-9ba9-4d0d-b0bb-e7e2055a8ff8_terseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueAdditions" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Additions</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueAdditions_label_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueAdditions" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Cost, Additions</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtAmortizedValueAdditions" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ServicingAssetAtAmortizedValueAdditions"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ServicingAssetAtAmortizedValueAdditions" xlink:to="lab_us-gaap_ServicingAssetAtAmortizedValueAdditions" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_6867dbd1-8ad4-41e4-abec-ace37d34b34d_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Transfers into Level 3</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3" xlink:to="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fbb86338-e1d1-492b-9f40-c0725ad3abcf_terseLabel_en-US" xlink:label="lab_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Instruments [Domain]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="lab_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DepreciationNonproduction_36d15d48-7d36-4e52-8975-5f51b1eb7f1b_terseLabel_en-US" xlink:label="lab_us-gaap_DepreciationNonproduction" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Depreciation of premises and equipment</link:label>
    <link:label id="lab_us-gaap_DepreciationNonproduction_738223e0-acfd-4c2b-abdc-f23ba56eeda7_verboseLabel_en-US" xlink:label="lab_us-gaap_DepreciationNonproduction" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Depreciation and amortization of properties and equipment</link:label>
    <link:label id="lab_us-gaap_DepreciationNonproduction_label_en-US" xlink:label="lab_us-gaap_DepreciationNonproduction" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Depreciation, Nonproduction</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DepreciationNonproduction" xlink:to="lab_us-gaap_DepreciationNonproduction" xlink:type="arc" order="1"/>
    <link:label id="lab_source_MortgageBankingIncomeMember_aa7082bb-0e3a-4895-a8a6-d91bcebd7428_terseLabel_en-US" xlink:label="lab_source_MortgageBankingIncomeMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage banking income</link:label>
    <link:label id="lab_source_MortgageBankingIncomeMember_label_en-US" xlink:label="lab_source_MortgageBankingIncomeMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage Banking Income [Member]</link:label>
    <link:label id="lab_source_MortgageBankingIncomeMember_documentation_en-US" xlink:label="lab_source_MortgageBankingIncomeMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents banking income in relation to mortgages.</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_MortgageBankingIncomeMember" xlink:to="lab_source_MortgageBankingIncomeMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProvisionForLoanLeaseAndOtherLosses_09add71c-7aeb-4fed-8ca4-33b8aa26453a_terseLabel_en-US" xlink:label="lab_us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Provision (recovery of provision)</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProvisionForLoanLeaseAndOtherLosses"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:to="lab_us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:type="arc" order="1"/>
    <link:label id="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer_81c2406b-a000-479d-b707-1ba6ffaad498_terseLabel_en-US" xlink:label="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum Capital Adequacy with Capital Buffer Amount</link:label>
    <link:label id="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer_label_en-US" xlink:label="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Tier One Risk Based Capital Required for Capital Adequacy with Capital Buffer</link:label>
    <link:label id="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer_documentation_en-US" xlink:label="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">The minimum amount of Tier 1 Risk Based Capital required for capital adequacy with capital buffer purposes under the regulatory framework for prompt corrective action.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer" xlink:href="source-20211231.xsd#source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer" xlink:to="lab_source_TierOneRiskBasedCapitalRequiredforCapitalAdequacywithCapitalBuffer" xlink:type="arc" order="1"/>
    <link:label id="lab_source_GrossInvestmentinOperatingLeaseFinancing_5acc652b-19ea-4fa0-8e04-5bd18084e44c_terseLabel_en-US" xlink:label="lab_source_GrossInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross investment in operating lease financing</link:label>
    <link:label id="lab_source_GrossInvestmentinOperatingLeaseFinancing_label_en-US" xlink:label="lab_source_GrossInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Investment in Operating Lease Financing</link:label>
    <link:label id="lab_source_GrossInvestmentinOperatingLeaseFinancing_documentation_en-US" xlink:label="lab_source_GrossInvestmentinOperatingLeaseFinancing" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount before accumulated depreciation of physical assets used in the normal conduct of business to produce goods and services subject to or available for lease.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_GrossInvestmentinOperatingLeaseFinancing" xlink:href="source-20211231.xsd#source_GrossInvestmentinOperatingLeaseFinancing"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_GrossInvestmentinOperatingLeaseFinancing" xlink:to="lab_source_GrossInvestmentinOperatingLeaseFinancing" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_EntityCentralIndexKey_993ea01c-16cc-4762-9e41-dbd0fc197fe7_terseLabel_en-US" xlink:label="lab_dei_EntityCentralIndexKey" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Central Index Key</link:label>
    <link:label id="lab_dei_EntityCentralIndexKey_label_en-US" xlink:label="lab_dei_EntityCentralIndexKey" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Entity Central Index Key</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityCentralIndexKey"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_EntityCentralIndexKey" xlink:to="lab_dei_EntityCentralIndexKey" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_84d24b39-2e6c-4de7-bd8c-f9865f7ce872_terseLabel_en-US" xlink:label="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Earnings Per Share</link:label>
    <link:label id="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_label_en-US" xlink:label="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="lab_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable_2f72a41a-513a-4cd7-83fe-078c262c6782_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Fair Value, Off-balance Sheet Risks [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Fair Value, Off-balance Sheet Risks [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="lab_us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_Capital_7aeb6b9a-2aa6-44da-8efb-b69212acb95a_terseLabel_en-US" xlink:label="lab_us-gaap_Capital" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Actual Amount</link:label>
    <link:label id="lab_us-gaap_Capital_label_en-US" xlink:label="lab_us-gaap_Capital" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Total Capital, Actual</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Capital" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Capital"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_Capital" xlink:to="lab_us-gaap_Capital" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_LeaseCost_6e6e32fc-e417-4d37-b5f5-f33bc8842173_totalLabel_en-US" xlink:label="lab_us-gaap_LeaseCost" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total operating lease cost</link:label>
    <link:label id="lab_us-gaap_LeaseCost_label_en-US" xlink:label="lab_us-gaap_LeaseCost" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Lease, Cost</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCost" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseCost"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LeaseCost" xlink:to="lab_us-gaap_LeaseCost" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems_cf703630-cd8b-454b-b501-7744b36a1ecc_terseLabel_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Borrowed funds and mandatorily redeemable securities</link:label>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems_label_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Long Term Debt and Mandatorily Redeemable Securities [Line Items]</link:label>
    <link:label id="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems_documentation_en-US" xlink:label="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems" xlink:href="source-20211231.xsd#source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems" xlink:to="lab_source_LongTermDebtAndMandatorilyRedeemableSecuritiesLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_0cc89c7d-f6a9-4357-a617-5e6032ade060_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Past Due [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financing Receivable, Past Due [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:to="lab_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:type="arc" order="1"/>
    <link:label id="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member_5c082dca-cc64-4f55-a4d3-6a6139830740_terseLabel_en-US" xlink:label="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">ESPP offering through June 2021</link:label>
    <link:label id="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member_label_en-US" xlink:label="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Employee Stock Purchase Plan Offering June 2018 Through June 2020 [Member]</link:label>
    <link:label id="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member_documentation_en-US" xlink:label="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the most recent employee stock purchase plan offering starting in June 2018 and ending at June 1, 2020.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member" xlink:href="source-20211231.xsd#source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member" xlink:to="lab_source_EmployeeStockPurchasePlanOfferingJune2018ThroughJune2020Member" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_638ce497-17c3-41db-aa00-94279afaaea8_terseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Premises and Equipment</link:label>
    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_label_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Property, Plant and Equipment Disclosure [Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:to="lab_us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible_78d80d79-0f17-4935-ab57-13a64c96caa6_terseLabel_en-US" xlink:label="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Minimum service period required to participate in Plan</link:label>
    <link:label id="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible_label_en-US" xlink:label="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Defined Contribution Plan, Requisite Period of Service to Become Eligible</link:label>
    <link:label id="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible_documentation_en-US" xlink:label="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the requisite service period of employees to become eligible to participate in the plan.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible" xlink:href="source-20211231.xsd#source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible" xlink:to="lab_source_DefinedContributionPlanRequisitePeriodOfServiceToBecomeEligible" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_CapitalToRiskWeightedAssets_139dcdda-ffbe-42fe-b699-7bf6c9f8eba0_terseLabel_en-US" xlink:label="lab_us-gaap_CapitalToRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Actual Ratio (as a percent)</link:label>
    <link:label id="lab_us-gaap_CapitalToRiskWeightedAssets_label_en-US" xlink:label="lab_us-gaap_CapitalToRiskWeightedAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Total Risk-Based Capital Ratio, Actual</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalToRiskWeightedAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CapitalToRiskWeightedAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CapitalToRiskWeightedAssets" xlink:to="lab_us-gaap_CapitalToRiskWeightedAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ProceedsFromRepaymentsOfCommercialPaper_2d793a78-fdaa-419e-a7f3-58b9bbd651e3_terseLabel_en-US" xlink:label="lab_us-gaap_ProceedsFromRepaymentsOfCommercialPaper" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in commercial paper</link:label>
    <link:label id="lab_us-gaap_ProceedsFromRepaymentsOfCommercialPaper_label_en-US" xlink:label="lab_us-gaap_ProceedsFromRepaymentsOfCommercialPaper" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Proceeds from (Repayments of) Commercial Paper</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfCommercialPaper" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromRepaymentsOfCommercialPaper"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ProceedsFromRepaymentsOfCommercialPaper" xlink:to="lab_us-gaap_ProceedsFromRepaymentsOfCommercialPaper" xlink:type="arc" order="1"/>
    <link:label id="lab_source_InternallyAssignedGrade7To12Member_8c252037-4655-42d7-a6ca-97492199532c_terseLabel_en-US" xlink:label="lab_source_InternallyAssignedGrade7To12Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Credit Quality Grades 7-12</link:label>
    <link:label id="lab_source_InternallyAssignedGrade7To12Member_label_en-US" xlink:label="lab_source_InternallyAssignedGrade7To12Member" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Internally Assigned Grade 7 to 12 [Member]</link:label>
    <link:label id="lab_source_InternallyAssignedGrade7To12Member_documentation_en-US" xlink:label="lab_source_InternallyAssignedGrade7To12Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents internally generated quality grades indicating the bottom end of quality rankings, such that a credit quality grade of 7 is defined as watch and contains greater than average credit risk; grade 8 credits are defined as having potential weaknesses that deserve management's close attention; grades 9 and 10 are considered substandard; grade 11 is doubtful; and grade 12 is a loss.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_InternallyAssignedGrade7To12Member" xlink:href="source-20211231.xsd#source_InternallyAssignedGrade7To12Member"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_InternallyAssignedGrade7To12Member" xlink:to="lab_source_InternallyAssignedGrade7To12Member" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_4c98bc41-ac6b-4cd1-ba12-66b0631b7a38_terseLabel_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unrealized Losses</link:label>
    <link:label id="lab_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract_label_en-US" xlink:label="lab_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="lab_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_srt_CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract_8f45c5c9-1264-4010-9e43-be0b1b781939_terseLabel_en-US" xlink:label="lab_srt_CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Condensed Financial Information Disclosure [Abstract]</link:label>
    <link:label id="lab_srt_CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract_label_en-US" xlink:label="lab_srt_CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Condensed Financial Information Disclosure [Abstract]</link:label>
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    <link:label id="lab_us-gaap_DerivativeAssetFairValueGrossLiability_f69d9d4d-8bab-458b-9961-6fc51adda3fe_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeAssetFairValueGrossLiability" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Amounts Offset in the Statement of Financial Condition</link:label>
    <link:label id="lab_us-gaap_DerivativeAssetFairValueGrossLiability_label_en-US" xlink:label="lab_us-gaap_DerivativeAssetFairValueGrossLiability" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Asset, Fair Value, Gross Liability</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueGrossLiability" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeAssetFairValueGrossLiability"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeAssetFairValueGrossLiability" xlink:to="lab_us-gaap_DerivativeAssetFairValueGrossLiability" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInContinuingOperations_cd60b808-6761-4ab8-b7ab-db9f8599cfa6_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInContinuingOperations" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net change in cash and cash equivalents</link:label>
    <link:label id="lab_us-gaap_NetCashProvidedByUsedInContinuingOperations_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInContinuingOperations" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Cash Provided by (Used in) Continuing Operations</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInContinuingOperations" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInContinuingOperations"/>
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    <link:label id="lab_us-gaap_OtherIncomeMember_93cfbdb7-086b-4ae2-acf9-6a2e4be18044_terseLabel_en-US" xlink:label="lab_us-gaap_OtherIncomeMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other income</link:label>
    <link:label id="lab_us-gaap_OtherIncomeMember_label_en-US" xlink:label="lab_us-gaap_OtherIncomeMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other Income [Member]</link:label>
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    <link:label id="lab_source_StockAwardPlansMember_0a700a19-a08f-4e72-bf0c-595cd38efb3b_verboseLabel_en-US" xlink:label="lab_source_StockAwardPlansMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock award plans</link:label>
    <link:label id="lab_source_StockAwardPlansMember_label_en-US" xlink:label="lab_source_StockAwardPlansMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock Award Plans [Member]</link:label>
    <link:label id="lab_source_StockAwardPlansMember_documentation_en-US" xlink:label="lab_source_StockAwardPlansMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the stock award plan, which forms a part of the entity's incentive plans.</link:label>
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    <link:label id="lab_us-gaap_TreasuryStockSharesAcquired_00b1e543-8d47-4e77-ba04-e180fb9033f6_terseLabel_en-US" xlink:label="lab_us-gaap_TreasuryStockSharesAcquired" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Common stock acquired for treasury, shares</link:label>
    <link:label id="lab_us-gaap_TreasuryStockSharesAcquired_label_en-US" xlink:label="lab_us-gaap_TreasuryStockSharesAcquired" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Treasury Stock, Shares, Acquired</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockSharesAcquired"/>
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    <link:label id="lab_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase_7d3495eb-effe-4eaa-99a8-3155876cca84_terseLabel_en-US" xlink:label="lab_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal funds purchased and securities sold under agreements to repurchase</link:label>
    <link:label id="lab_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase_label_en-US" xlink:label="lab_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Federal Funds Purchased and Securities Sold under Agreements to Repurchase</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:to="lab_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase" xlink:type="arc" order="1"/>
    <link:label id="lab_dei_TradingSymbol_1d9e6441-2b47-422e-80e0-d1f1bf8dc44d_terseLabel_en-US" xlink:label="lab_dei_TradingSymbol" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trading Symbol</link:label>
    <link:label id="lab_dei_TradingSymbol_label_en-US" xlink:label="lab_dei_TradingSymbol" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Trading Symbol</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_TradingSymbol"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dei_TradingSymbol" xlink:to="lab_dei_TradingSymbol" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_eeab72f6-4f1d-4ad1-9af1-ffd893294794_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Long Lived Assets Held-for-sale [Table]</link:label>
    <link:label id="lab_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_label_en-US" xlink:label="lab_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Long Lived Assets Held-for-sale [Table]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable" xlink:to="lab_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueFairValue_637fe2f7-e40c-4f64-aacf-9277679d48bd_terseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair value of mortgage servicing rights at end of period</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueFairValue_label_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Cost, Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtAmortizedValueFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ServicingAssetAtAmortizedValueFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ServicingAssetAtAmortizedValueFairValue" xlink:to="lab_us-gaap_ServicingAssetAtAmortizedValueFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeAssets_14b82ea4-e379-4c6e-9f06-7ec216eaafb9_totalLabel_en-US" xlink:label="lab_us-gaap_DerivativeAssets" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Net Amounts of Assets Presented in the Statement of Financial Condition</link:label>
    <link:label id="lab_us-gaap_DerivativeAssets_label_en-US" xlink:label="lab_us-gaap_DerivativeAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Asset</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeAssets" xlink:to="lab_us-gaap_DerivativeAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DeferredTaxLiabilitiesOther_21c608b8-fb2b-4ca4-9fed-8d13dc26bd29_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredTaxLiabilitiesOther" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Other</link:label>
    <link:label id="lab_us-gaap_DeferredTaxLiabilitiesOther_label_en-US" xlink:label="lab_us-gaap_DeferredTaxLiabilitiesOther" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Deferred Tax Liabilities, Other</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesOther" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxLiabilitiesOther"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DeferredTaxLiabilitiesOther" xlink:to="lab_us-gaap_DeferredTaxLiabilitiesOther" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems_75132bde-1d86-4e63-8dba-b8af0163d317_terseLabel_en-US" xlink:label="lab_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]</link:label>
    <link:label id="lab_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems_label_en-US" xlink:label="lab_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="lab_us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_651eb09e-31cd-492d-aa4e-588345f0e52e_negatedTotalLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Total unrealized losses</link:label>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_label_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:to="lab_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_0f684abc-12fb-486e-af53-de9a5d81942a_negatedLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Change in other assets</link:label>
    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Increase (Decrease) in Other Operating Assets</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:to="lab_us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueGrossAsset_578b1f14-1b4a-487d-a833-6601e4b3aeb5_terseLabel_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross Amounts Offset in the Statement of Financial Condition</link:label>
    <link:label id="lab_us-gaap_DerivativeLiabilityFairValueGrossAsset_label_en-US" xlink:label="lab_us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Liability, Fair Value, Gross Asset</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:to="lab_us-gaap_DerivativeLiabilityFairValueGrossAsset" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized_5aa43c3d-baef-493d-875b-c9d4f7d6edac_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">To Be Well Capitalized Under Prompt Corrective Action Provisions Amount</link:label>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized_label_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Tier One Leverage Capital, Well Capitalized, Minimum</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized"/>
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    <link:label id="lab_us-gaap_LessorLeasesPolicyTextBlock_66d55e84-38e3-48dd-9ae4-351c2aa3fd50_terseLabel_en-US" xlink:label="lab_us-gaap_LessorLeasesPolicyTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Equipment Owned Under Operating Leases</link:label>
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    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearTwo_documentation_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationInYearTwo" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the amount of expense to be charged against earnings in the year two following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.</link:label>
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    <link:label id="lab_source_Lessordirectfinanceleaseunearnedincome_5874867a-165e-4f5b-8f14-11656202aa45_negatedLabel_en-US" xlink:label="lab_source_Lessordirectfinanceleaseunearnedincome" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Less: unearned income</link:label>
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    <link:label id="lab_us-gaap_LiabilitiesFairValueDisclosureAbstract_6851f691-bf80-4921-b08b-1f7597b0fade_terseLabel_en-US" xlink:label="lab_us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liabilities:</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
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    <link:label id="lab_us-gaap_AllocatedShareBasedCompensationExpense_7cad8d44-91a8-4955-970b-bc7463aadeed_terseLabel_en-US" xlink:label="lab_us-gaap_AllocatedShareBasedCompensationExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Stock-based compensation expense</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
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    <link:label id="lab_us-gaap_IntangibleAssetsNetIncludingGoodwill_9ee3dac0-f270-4962-9773-7ce8b4a8c529_terseLabel_en-US" xlink:label="lab_us-gaap_IntangibleAssetsNetIncludingGoodwill" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Goodwill and intangible assets</link:label>
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    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearTwo_af61bbc1-bf48-4aba-a3c7-a0945a150e0d_terseLabel_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearTwo" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2023</link:label>
    <link:label id="lab_us-gaap_TimeDepositMaturitiesYearTwo_label_en-US" xlink:label="lab_us-gaap_TimeDepositMaturitiesYearTwo" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Time Deposit Maturities, Year Two</link:label>
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    <link:label id="lab_us-gaap_LaborAndRelatedExpense_0da651d2-3cde-4be4-9442-0142e062f2d6_terseLabel_en-US" xlink:label="lab_us-gaap_LaborAndRelatedExpense" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Salaries and employee benefits</link:label>
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    <link:label id="lab_us-gaap_InvestmentTypeCategorizationMember_d764026d-5f8e-4363-8b56-82dc19bee4dd_verboseLabel_en-US" xlink:label="lab_us-gaap_InvestmentTypeCategorizationMember" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investments [Domain]</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
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    <link:label id="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_021e2d74-ef3e-4c77-8b0c-5d2ac43842a0_periodStartLabel_en-US" xlink:label="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and cash equivalents, beginning of year</link:label>
    <link:label id="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_c10b6d46-8b14-4a47-847f-e0ef3d683dc8_periodEndLabel_en-US" xlink:label="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash and cash equivalents, end of year</link:label>
    <link:label id="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_label_en-US" xlink:label="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:to="lab_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:type="arc" order="1"/>
    <link:label id="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation_91af1196-364f-4e38-ab0e-44102146799d_terseLabel_en-US" xlink:label="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of reportable units used in goodwill allocation</link:label>
    <link:label id="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation_label_en-US" xlink:label="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of Reportable Units Used for Goodwill Allocation</link:label>
    <link:label id="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation_documentation_en-US" xlink:label="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Number of reportable units used to categorize goodwill allocation.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_NumberOfReportableUnitsUsedForGoodwillAllocation" xlink:href="source-20211231.xsd#source_NumberOfReportableUnitsUsedForGoodwillAllocation"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_NumberOfReportableUnitsUsedForGoodwillAllocation" xlink:to="lab_source_NumberOfReportableUnitsUsedForGoodwillAllocation" xlink:type="arc" order="1"/>
    <link:label id="lab_source_SummaryOfSignificantAccountingPoliciesLineItems_00cc4de0-e767-4692-92f6-94c3564e8d66_terseLabel_en-US" xlink:label="lab_source_SummaryOfSignificantAccountingPoliciesLineItems" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accounting Policies</link:label>
    <link:label id="lab_source_SummaryOfSignificantAccountingPoliciesLineItems_label_en-US" xlink:label="lab_source_SummaryOfSignificantAccountingPoliciesLineItems" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Summary of Significant Accounting Policies [Line Items]</link:label>
    <link:label id="lab_source_SummaryOfSignificantAccountingPoliciesLineItems_documentation_en-US" xlink:label="lab_source_SummaryOfSignificantAccountingPoliciesLineItems" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">-- None. No documentation exists for this element. --</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_SummaryOfSignificantAccountingPoliciesLineItems" xlink:href="source-20211231.xsd#source_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="lab_source_SummaryOfSignificantAccountingPoliciesLineItems" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_de210df2-57de-4aa2-a056-2e94a09a57b0_terseLabel_en-US" xlink:label="lab_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Comprehensive Income [Abstract]</link:label>
    <link:label id="lab_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_label_en-US" xlink:label="lab_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Statement of Comprehensive Income [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:to="lab_us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsGross_7d5197db-c3fd-4560-bb92-3dd47a2afd7d_terseLabel_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Gross carrying amount</link:label>
    <link:label id="lab_us-gaap_FiniteLivedIntangibleAssetsGross_label_en-US" xlink:label="lab_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Finite-Lived Intangible Assets, Gross</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:to="lab_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain_1f63bfbd-89c7-455b-8c8b-3a6e7211d891_terseLabel_en-US" xlink:label="lab_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Instruments Subject to Mandatory Redemption, Financial Instrument [Domain]</link:label>
    <link:label id="lab_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain_label_en-US" xlink:label="lab_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Financial Instruments Subject to Mandatory Redemption, Financial Instrument [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain" xlink:to="lab_us-gaap_SharesSubjectToMandatoryRedemptionFinancialInstrumentDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_c23a3201-581f-462f-803b-b9741e3b187d_terseLabel_en-US" xlink:label="lab_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Summary of core deposit intangible and other intangible assets</link:label>
    <link:label id="lab_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_label_en-US" xlink:label="lab_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of Finite-Lived Intangible Assets [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock" xlink:to="lab_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_source_LoansReceivableDeferredIncomePPPLoans_076ee0a8-aa45-4028-b4ef-f6367aa3fa70_terseLabel_en-US" xlink:label="lab_source_LoansReceivableDeferredIncomePPPLoans" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">PPP loans receivable deferred income</link:label>
    <link:label id="lab_source_LoansReceivableDeferredIncomePPPLoans_label_en-US" xlink:label="lab_source_LoansReceivableDeferredIncomePPPLoans" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">LoansReceivableDeferredIncomePPPLoans</link:label>
    <link:label id="lab_source_LoansReceivableDeferredIncomePPPLoans_documentation_en-US" xlink:label="lab_source_LoansReceivableDeferredIncomePPPLoans" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of deferred interest and fee income and unamortized costs incurred to originate PPP loans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_LoansReceivableDeferredIncomePPPLoans" xlink:href="source-20211231.xsd#source_LoansReceivableDeferredIncomePPPLoans"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_LoansReceivableDeferredIncomePPPLoans" xlink:to="lab_source_LoansReceivableDeferredIncomePPPLoans" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleRestricted_1cabef48-5090-454d-89e0-9ec1895d5714_terseLabel_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Investment securities pledged as collateral</link:label>
    <link:label id="lab_us-gaap_DebtSecuritiesAvailableForSaleRestricted_label_en-US" xlink:label="lab_us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Available-for-sale, Restricted</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleRestricted"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:to="lab_us-gaap_DebtSecuritiesAvailableForSaleRestricted" xlink:type="arc" order="1"/>
    <link:label id="lab_source_MediumAndHeavyDutyTruckMember_a1f8ed62-88e0-4156-9e4f-62d734d7b912_terseLabel_en-US" xlink:label="lab_source_MediumAndHeavyDutyTruckMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Medium and heavy duty truck</link:label>
    <link:label id="lab_source_MediumAndHeavyDutyTruckMember_label_en-US" xlink:label="lab_source_MediumAndHeavyDutyTruckMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Medium and Heavy Duty Truck [Member]</link:label>
    <link:label id="lab_source_MediumAndHeavyDutyTruckMember_documentation_en-US" xlink:label="lab_source_MediumAndHeavyDutyTruckMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Class of financing receivables related to medium and heavy duty truck loans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_MediumAndHeavyDutyTruckMember" xlink:href="source-20211231.xsd#source_MediumAndHeavyDutyTruckMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_MediumAndHeavyDutyTruckMember" xlink:to="lab_source_MediumAndHeavyDutyTruckMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_b3690197-bac4-4ff6-a82b-419b94ce114d_terseLabel_en-US" xlink:label="lab_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Unrealized (depreciation) appreciation of investment securities available-for-sale</link:label>
    <link:label id="lab_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_label_en-US" xlink:label="lab_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:to="lab_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax" xlink:type="arc" order="1"/>
    <link:label id="lab_source_CommercialAndAgriculturalLoansMember_84035b26-c274-41fc-8a86-cc5c1f9e5ffb_terseLabel_en-US" xlink:label="lab_source_CommercialAndAgriculturalLoansMember" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial and agricultural</link:label>
    <link:label id="lab_source_CommercialAndAgriculturalLoansMember_label_en-US" xlink:label="lab_source_CommercialAndAgriculturalLoansMember" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Commercial and Agricultural Loans [Member]</link:label>
    <link:label id="lab_source_CommercialAndAgriculturalLoansMember_documentation_en-US" xlink:label="lab_source_CommercialAndAgriculturalLoansMember" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Class of financing receivables related to commercial and agricultural loans.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_CommercialAndAgriculturalLoansMember" xlink:href="source-20211231.xsd#source_CommercialAndAgriculturalLoansMember"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_CommercialAndAgriculturalLoansMember" xlink:to="lab_source_CommercialAndAgriculturalLoansMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_c5dc489e-e05c-42aa-baf4-52cde2dd41e8_terseLabel_en-US" xlink:label="lab_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period</link:label>
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    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:to="lab_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:type="arc" order="1"/>
    <link:label id="lab_source_SubordinatedNoteIssuedinJune2007Member_291e0093-d092-4934-8629-0dbfe9cb6f41_terseLabel_en-US" xlink:label="lab_source_SubordinatedNoteIssuedinJune2007Member" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">June 2007 issuance</link:label>
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    <link:label id="lab_source_SubordinatedNoteIssuedinJune2007Member_documentation_en-US" xlink:label="lab_source_SubordinatedNoteIssuedinJune2007Member" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents information pertaining to subordinated notes issued in June, 2007.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_SubordinatedNoteIssuedinJune2007Member" xlink:href="source-20211231.xsd#source_SubordinatedNoteIssuedinJune2007Member"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_SubordinatedNoteIssuedinJune2007Member" xlink:to="lab_source_SubordinatedNoteIssuedinJune2007Member" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_0b66c2c7-b7af-4bfb-9e21-81b3ab6202d1_periodStartLabel_en-US" xlink:label="lab_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance at the beginning of the period</link:label>
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    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_BuildingAndBuildingImprovementsMember" xlink:to="lab_us-gaap_BuildingAndBuildingImprovementsMember" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets_34371d1b-053d-4b6a-8c45-9d91b04cbd6c_terseLabel_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio (as a percent)</link:label>
    <link:label id="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets_label_en-US" xlink:label="lab_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Banking Regulation, Tier One Leverage Capital Ratio, Well Capitalized, Minimum</link:label>
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    <link:label id="lab_source_DeferredTaxAssetsOperatingLeaseLiability_233a293b-a901-4653-b90c-fda13453bcce_terseLabel_en-US" xlink:label="lab_source_DeferredTaxAssetsOperatingLeaseLiability" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Operating lease liability</link:label>
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    <link:label id="lab_source_DeferredTaxAssetsOperatingLeaseLiability_documentation_en-US" xlink:label="lab_source_DeferredTaxAssetsOperatingLeaseLiability" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount, before allocation of valuation allowances, of deferred tax asset attributable to deductible temporary differences from operating lease liabilities.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_DeferredTaxAssetsOperatingLeaseLiability" xlink:href="source-20211231.xsd#source_DeferredTaxAssetsOperatingLeaseLiability"/>
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    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward_d96912e6-a4bd-468b-afd1-a82c27f0a6d5_terseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Changes in mortgage servicing rights</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward_label_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Cost, Balance [Roll Forward]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward" xlink:to="lab_us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_HeldToMaturitySecurities_672e1ce6-811c-4ef8-ad3b-30b0835b8f3c_terseLabel_en-US" xlink:label="lab_us-gaap_HeldToMaturitySecurities" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Held-to-maturity investment securities</link:label>
    <link:label id="lab_us-gaap_HeldToMaturitySecurities_label_en-US" xlink:label="lab_us-gaap_HeldToMaturitySecurities" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecurities" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_HeldToMaturitySecurities"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_HeldToMaturitySecurities" xlink:to="lab_us-gaap_HeldToMaturitySecurities" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_97e032d6-9d36-4e68-a9d1-dda963028700_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Vested (in dollars per share)</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:to="lab_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_1b0d5f13-ca21-4622-8d11-2a8bd1eb03e0_terseLabel_en-US" xlink:label="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Subordinated notes</link:label>
    <link:label id="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_c2f37ccd-b830-499b-aaba-d78b7e790dc5_verboseLabel_en-US" xlink:label="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Amount of subordinated notes</link:label>
    <link:label id="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust_label_en-US" xlink:label="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:to="lab_us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValue_5a37acdf-4422-4eee-bc64-0f99500c2d2d_periodStartLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValue" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Balance at the beginning of the period</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValue_9a69e12a-cf11-481d-a302-6da7c4a28d4e_periodEndLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValue" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Carrying value before valuation allowance at end of year</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValue_fe163dd7-5c77-492f-9173-25d786a22e9a_terseLabel_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValue" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage servicing rights</link:label>
    <link:label id="lab_us-gaap_ServicingAssetAtAmortizedValue_label_en-US" xlink:label="lab_us-gaap_ServicingAssetAtAmortizedValue" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Cost</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtAmortizedValue" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ServicingAssetAtAmortizedValue"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ServicingAssetAtAmortizedValue" xlink:to="lab_us-gaap_ServicingAssetAtAmortizedValue" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DebtInstrumentNameDomain_4adb3b94-f963-4d68-81a4-63ea3f0ba2d8_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentNameDomain" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument, Name [Domain]</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentNameDomain_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentNameDomain" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Debt Instrument, Name [Domain]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentNameDomain" xlink:to="lab_us-gaap_DebtInstrumentNameDomain" xlink:type="arc" order="1"/>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent_e64c62e7-5f28-4102-bb0a-49bc10be99ea_terseLabel_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">2022</link:label>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent_label_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Servicing Asset at Amortized Value Expected Amortization Current</link:label>
    <link:label id="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent_documentation_en-US" xlink:label="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Represents the amount of expense to be charged against earnings in the next fiscal year following the latest balance sheet date, for the periodic recognition of servicing assets relative to estimated net servicing income.</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent" xlink:href="source-20211231.xsd#source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent" xlink:to="lab_source_ServicingAssetAtAmortizedValueExpectedAmortizationCurrent" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_MortgageServicingRightsMSRImpairmentRecovery_2c535c3a-5ba1-4d4a-8e13-91d3627f0272_terseLabel_en-US" xlink:label="lab_us-gaap_MortgageServicingRightsMSRImpairmentRecovery" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage servicing rights (recoveries) impairments</link:label>
    <link:label id="lab_us-gaap_MortgageServicingRightsMSRImpairmentRecovery_label_en-US" xlink:label="lab_us-gaap_MortgageServicingRightsMSRImpairmentRecovery" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Mortgage Servicing Rights (MSR) Impairment (Recovery)</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageServicingRightsMSRImpairmentRecovery" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MortgageServicingRightsMSRImpairmentRecovery"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_MortgageServicingRightsMSRImpairmentRecovery" xlink:to="lab_us-gaap_MortgageServicingRightsMSRImpairmentRecovery" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_AlternativeInvestmentMeasurementInput_5b10af12-e507-44ce-aef5-c53cfaed719f_terseLabel_en-US" xlink:label="lab_us-gaap_AlternativeInvestmentMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Discount rate (as a percent)</link:label>
    <link:label id="lab_us-gaap_AlternativeInvestmentMeasurementInput_label_en-US" xlink:label="lab_us-gaap_AlternativeInvestmentMeasurementInput" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Alternative Investment, Measurement Input</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AlternativeInvestmentMeasurementInput" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AlternativeInvestmentMeasurementInput"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AlternativeInvestmentMeasurementInput" xlink:to="lab_us-gaap_AlternativeInvestmentMeasurementInput" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_IncomeTaxUncertaintiesAbstract_2a70182a-b62e-4738-a7c4-9fe23abe0f0b_terseLabel_en-US" xlink:label="lab_us-gaap_IncomeTaxUncertaintiesAbstract" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income taxes</link:label>
    <link:label id="lab_us-gaap_IncomeTaxUncertaintiesAbstract_label_en-US" xlink:label="lab_us-gaap_IncomeTaxUncertaintiesAbstract" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Income Tax Uncertainties [Abstract]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxUncertaintiesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxUncertaintiesAbstract"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_IncomeTaxUncertaintiesAbstract" xlink:to="lab_us-gaap_IncomeTaxUncertaintiesAbstract" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_OffsettingLiabilitiesTableTextBlock_b9d5362f-05f7-41fc-abaf-ebd633fc7bee_terseLabel_en-US" xlink:label="lab_us-gaap_OffsettingLiabilitiesTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Schedule of offsetting of financial liabilities and derivative liabilities</link:label>
    <link:label id="lab_us-gaap_OffsettingLiabilitiesTableTextBlock_label_en-US" xlink:label="lab_us-gaap_OffsettingLiabilitiesTableTextBlock" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Offsetting Liabilities [Table Text Block]</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffsettingLiabilitiesTableTextBlock" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OffsettingLiabilitiesTableTextBlock"/>
    <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OffsettingLiabilitiesTableTextBlock" xlink:to="lab_us-gaap_OffsettingLiabilitiesTableTextBlock" xlink:type="arc" order="1"/>
    <link:label id="lab_us-gaap_DerivativeFairValueOfDerivativeLiability_57dc4291-7eec-46db-8e41-722b1b0923db_netLabel_en-US" xlink:label="lab_us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:role="http://www.xbrl.org/2009/role/netLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Liability derivatives, Fair value</link:label>
    <link:label id="lab_us-gaap_DerivativeFairValueOfDerivativeLiability_27589d03-92f2-45a8-ad4d-505c87842bc7_verboseLabel_en-US" xlink:label="lab_us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Accrued expenses and other liabilities</link:label>
    <link:label id="lab_us-gaap_DerivativeFairValueOfDerivativeLiability_label_en-US" xlink:label="lab_us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en-US">Derivative Liability, Fair Value, Gross Liability</link:label>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
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