Is it permissible to return a borrowed sum in dollars at the exchange rate at the time of borrowing, instead of the exchange rate at the time of repayment, given that the borrower intended to share the profit with the lender?

It is permissible for the creditor to return more than what is due to the debtor upon repayment, out of kindness, provided that this is not stipulated as a condition.

As for repaying the debt with a different currency, it is permissible by mutual agreement of both parties, at the rate of the day of repayment. This is the opinion of the majority of jurists. They cite as evidence the Hadith of Abdullah ibn Umar (may Allah be pleased with them both) who said: "There is no harm in taking them at their rate of the day, as long as you do not separate while there is still something between you." It is stipulated that the repayment must be immediate.

Some scholars have disagreed with this condition, permitting repayment in a different currency at its rate of the day or otherwise, as long as it is hand-to-hand.

It is more prudent to avoid repaying debts with a different currency in the future to avoid disagreement, while it is permissible to show kindness to the creditor by giving them more than what is due.