Musnad Ahmad 314

It was narrated that Malik bin Aws bin al-Hadathan said: l brought some dinars of mine and wanted to exchange them. Talhah bin ‘Ubaidullah met me and we agreed to an exchange. Then he took them and said: Wait until my storekeeper comes - Abu `Amir said. From al-Ghalal (a place). And he said concerning it. All of it should be ‘Take this’ and `take this` [i.e., exchanged on the spot]. - I asked ‘Umar bin al-Khattab (رضي الله عنه) about that and he said: I heard the Messenger of Allah (ﷺ) say: `Silver for gold is riba, unless it is exchanged on the spot, wheat for wheat is riba, unless it is exchanged on the spot; barley for barley is riba, unless it is exchanged on the spot dates for dates is ribu unless it is exchanged on the spot.”