Is QARZ-E-HASANA (loan without profit) is compulsory to return to the owner in any circumstances. 2nd is that can a borrower of QARZ-HASANA return some extra amount in addition to the actual amount only and only with his own will.
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If the creditor did not set a condition on the debtor to repay the debt with a price that is more than its original price, then there is no harm on the debtor to repay the debts with an additional price with the objective of being kind to the creditor. It is reported in an narration that "The best people are those who repay their debts in a best way."
Allaah knows best.
You can search for fatwa through many choices