Musannaf Ibn Abi Shayba 13:2807

Abu Bakr narrated to us, he said: Ghundar narrated to us, from Shu'bah, from al-Hakam and Hammad, he said: I asked them both about a man who lends a man a dirham, then he takes [back] better than what he gave. They both said: "If he did not intend [it at the time of the loan], then there is no harm."