Dhakwan says that once Abu Sa'id Khudri (may Allah be pleased with him) sent me to Ibn Abbas (may Allah be pleased with both of them) to ask: Regarding what you say about the transaction of sarf (exchange of gold and silver), do you find its evidence in the Qur'an or have you heard anything about it from the Prophet (peace and blessings of Allah be upon him)? He replied: I have not found this matter in the Book of Allah, nor have I heard it directly from the Prophet (peace and blessings of Allah be upon him), but Usama bin Zaid (may Allah be pleased with him) informed me that the Prophet (peace and blessings of Allah be upon him) said: Riba (usury) is related to credit.