Indeed returning the debt with some extra-money
besides the principal amount is a very gracious thing on the part of the
borrower. It is his expression of gratitude towards the lender. Today this is
perhaps much more desirable because of inflation. The money he borrows gets
depreciated because of inflation and hence if he repays over and above, he might
be in fact making up for this loss caused to the lender.
In this regard, however, it should remain clear that this
extra amount is merely a favour from the borrower. In no case, should a lender
demand an extra amount because this would amount to charging interest on his
part, which of course is forbidden.