What is the ruling on accepting a bank reward deposited into a current account after withdrawing the full amount or leaving a small amount? Is it permissible to take it since the bank was not borrowing at that time? Is it better not to fulfill the condition for the reward, or to donate it if benefiting from it is unlawful?

Gifts to a current account are prohibited because it is a loan, and a gift from a borrower to a lender is forbidden unless it is deducted from the debt or was customary between them before the loan. The bonus offered by the bank for depositing in a current account is forbidden, whether before or after the repayment of the loan, because it is considered a stipulated condition and thus riba (usury). This bonus must be returned and is not permissible to accept. Ibn Qudamah stated that any loan conditioned upon an increase or a gift is unlawful, and that the Companions (may Allah be pleased with them) used to refuse gifts from borrowers fearing usury.