What is the ruling on the amount of money a man kept for himself from his father's and mother's money? Should it be returned to the father—who deals in usury—or to his brother? Should it be returned as the original amount, or with the interest of twenty years, or at the rate of increase in real estate values, or is it considered a debt to be repaid only as the original amount?

If a father sends money to his son as a loan to complete his studies, this money becomes a debt owed by the son in the currency he received. If the son returns with money in the same foreign currency, he must repay his father an amount equivalent to the loan, and he may keep any surplus, if there is any. The debt must be repaid in like kind, without considering any potential profits from investing it, because that would be usury (riba). It is recommended to advise the father to repent from engaging in usurious transactions.