Sunan al-Shafi'i

It is narrated from Abu Nadrah (may Allah have mercy on him) that I was sitting with Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) when a man pressed me from behind and said, "Ask Abu Sa'id (may Allah be pleased with him) whether it is permissible to trade silver for silver with an increase or decrease (in amount)?" I said to Sayyiduna Abu Sa'id (may Allah be pleased with him), "This man is telling me to ask you about the issue of trading silver for silver." Abu Sa'id (may Allah be pleased with him) said, "That is usury (riba)." The man said, "Now ask, is this your personal opinion or did you hear it from the Messenger of Allah (peace and blessings be upon him)?" I said to Sayyiduna Abu Sa'id (may Allah be pleased with him), "He is asking whether this is your own view or a hadith of the Messenger of Allah (peace and blessings be upon him)?" Sayyiduna Abu Sa'id (may Allah be pleased with him) said, "I have narrated what I witnessed in the gathering of the Messenger of Allah (peace and blessings be upon him): A man who had dates brought one sa' of good quality dates, so the Messenger of Allah (peace and blessings be upon him) said to him, 'These seem to be of better quality than our dates.' The man said, 'I exchanged two sa' of my dates for one sa' of these.' The Messenger of Allah (peace and blessings be upon him) said, 'You have engaged in a usurious transaction.' The man said, 'O Messenger of Allah, the price of these in the market is such and such, and the market rate of our dates is such and such.' The Prophet (peace and blessings be upon him) said, 'Sell your dates for a price, then buy the ones you like with that price.' Sayyiduna Abu Sa'id (may Allah be pleased with him) said, 'If there is usury in dates, then why would there not be usury in silver?'"