Sayyiduna Abu Hurayrah and Sayyiduna Abu Sa'id (may Allah be pleased with them both) both said that the Messenger of Allah (peace and blessings be upon him) appointed a man of Banu Adi of the Ansar as governor over Khaybar. He came with fine-quality dates, and he (peace and blessings be upon him) asked: "Are all the dates of Khaybar like this?" He said: No, O Messenger of Allah! We take one sa' (of these) for two sa's of mixed dates. The Prophet (peace and blessings be upon him) said: "Do not do that; rather (exchange) equal for equal, or sell these and buy those with their price. And the same applies to what is weighed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10518
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) held that excess (tafadul) in exchange (sarf) was permissible and saw no harm in it. When he met Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him), Sayyiduna Abu Sa'id (may Allah be pleased with him) said: O Ibn Abbas! Do you not fear Allah? How long will you go on making people consume usury? Has it not reached you that one day the Prophet (peace and blessings be upon him) was with his wife Sayyidah Umm Salamah (may Allah be pleased with her) and he (peace and blessings be upon him) said: "I would love to eat Ajwah dates." So Sayyidah Umm Salamah (may Allah be pleased with her) sent two sa's of old dates to the house of a man of the Ansar, and in exchange she received one sa' of Ajwah dates. She presented them to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) liked them very much. He (peace and blessings be upon him) picked up a date, then stopped. He (peace and blessings be upon him) asked: "Where did you get these?" Sayyidah Umm Salamah (may Allah be pleased with her) said: I sent two sa's of old dates to so-and-so's house, and this one sa' came in exchange for them. He (peace and blessings be upon him) threw the date from his hand and said: "Return it, return it; I have no need of it. Dates for dates, wheat for wheat, barley for barley, gold for gold, silver for silver — it must be equal for equal and hand to hand; no increase or decrease in it is right. Whoever gives more or less has taken usury — (and so it is with) everything that is weighed or measured." Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: O Abu Sa'id! You have reminded me of a matter that I had forgotten; I seek Allah's forgiveness and repent to Him. After that he used to forbid it most strictly.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10519
Hayyan bin Ubaydullah said: Abu Mijlaz (may Allah have mercy on him) was asked about exchange (sarf) of money while I was present, and Abu Mijlaz Lahiq bin Humayd (may Allah have mercy on him) said: For a period of his life Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) used to say that when it is in cash there is no harm, and he used to say that usury is only in credit transactions, until he met Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him), who mentioned the hadith in a similar way: that the Prophet (peace and blessings be upon him) said: "Like must be for like, equally; whoever gives more, that is usury; and everything that is weighed or measured is likewise." Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: "O Abu Sa'id! 'Jazak Allahu khayran' (may Allah reward you with good) — may He grant you Paradise on my behalf. You have reminded me of something I had forgotten. 'Astaghfirullaha wa atubu ilayh' (I seek Allah's forgiveness and repent to Him)." And after that he used to forbid it most strictly.
Abu Ahmad (Ibn Adi) said: Only Hayyan narrates this hadith from Abu Mijlaz. Hayyan has been criticised (by the hadith critics).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10520
Al-Zuhri (may Allah have mercy on him) said that Sa'id bin al-Musayyib (may Allah have mercy on him) said: Usury is only in gold and silver, or in things that are measured or weighed and that relate to eating and drinking.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10521