Is it considered usury to repay a sum that a brother borrowed from an Islamic bank and then lent to the questioner, with the addition of a certain percentage (half the bank's profit rate) upon repayment?

If the increase in a loan is stipulated or implicitly agreed upon, it is impermissible because it is usury (riba). Scholars have unanimously agreed that for a lender to stipulate an increase or a gift from the borrower is usury. However, if the increase is not stipulated and you wish to repay the debt with something better, this is commendable, for the Prophet, peace and blessings be upon him, said: "The best among you are those who are best in repaying debts."