179:14 If one person knows that he owes money to another but the other says, "I am sure you don't owe me anything," then he is exempt from paying. This is because the lender forgives the debt.

179:15 If a borrower goes to repay a lender through a messenger, as soon as he gives the money to the messenger, the messenger acquires it on behalf of the lender. Therefore, if the borrower regrets handing the money over and wants to take it back from the messenger and repay the debt later, it is prohibited. Since the money is already considered as back in the lender's possession, returning it to the borrower would be like the messenger lending the money to the borrower without the lender's knowledge, which is forbidden.