What is the ruling of Islamic law regarding a creditor's refusal to accept repayment of a debt in a currency other than the one agreed upon, given the debtor's inability to provide the agreed-upon currency except at an exorbitant price?

The loan must be repaid in Riyals as it was taken, even if its exchange rate against the Egyptian Pound has risen, because what is obligatory in repaying a loan is its equivalent. It is not permissible to link fixed debts to the price level. There is no usury or injustice in this; rather, it is justice, and the doer of good should be rewarded with good. The Messenger of Allah, peace and blessings be upon him, said: "Indeed, the best of people are those who are best in fulfilling their obligations."