Is it permissible to repay a debt to its owner with an increase if the owner of the debt did not stipulate that?

Question:
May Allah reward you, Your Eminence, father. The questioner says: I borrowed five thousand riyals from a person, and I want to return them to him with an increase of two thousand riyals, and he did not stipulate that; rather, it is a reward from me to him. Is that permissible?

Answer:
Yes, if this condition was not present and it is merely out of good character in repaying, there is no harm. This is good character in repaying, and the Prophet (peace and blessings be upon him) encouraged good character in repaying. What is forbidden is if the lender stipulates, saying, "I only lent on the condition of an increase." This is riba (usury or interest) and is not permissible by scholarly consensus.