Musannaf Ibn Abi Shayba 13:1058

Abu Bakr narrated to us, he said: Mu'tamir ibn Sulayman narrated to us, from Layth, from Tawus, who said: If the basis of the right is a debt [from a sale], then do not take for it anything except what you sold it for. But if it is a loan, then it does not harm you to take [back] other than what you loaned.