It is permissible to waive part of a debt in return for bringing forward repayment.

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Check below answers in case you are looking for other related questions:
Delaying repayment of a bank loan so that they will waive the interest
Should he claim bankruptcy so that interest charges will be waived from him?

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Related Answers:
Ruling on buying by hire-purchase
Giving a loan with a penalty clause
Is delay in repayment of the debt regarded as charity on the part of the creditor?
Delaying repayment of a bank loan so that they will waive the interest
Should he claim bankruptcy so that interest charges will be waived from him?

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