Is it permissible for the creditor to demand 100,0 pounds as a reward, knowing that the original amount of the debt was 735,0 pounds, and the creditor bought the house, which was the origin of the debt, for 900,0 pounds? Does he have the right to take this reward, and what is the ruling of Sharia on this transaction?

A loan is a contract of donation intended to seek reward from Allah, and it is not permissible to stipulate an increase over the principal amount at the time of the contract or before it, because that is usury (riba). A stipulated increase in return for time is forbidden. Even if the increase is in the form of a promise, it is prohibited, because the consideration in contracts is based on intentions. The Sharia (definition) has permitted the borrower to give an increase upon repayment without prior agreement, as a gesture of kindness, as reported from the Prophet, peace and blessings be upon him: "The best among you are those who are best in settling debts." Therefore, the lender is entitled to no more than the money he lent, and it is not permissible for him to demand more than that based on a prior promise.