Musannaf Ibn Abi Shayba 13:2551

Abu Bakr narrated to us, he said: Ghundar narrated to us, from Hisham, from al-Hasan and Ibn Sirin, they both said: "If you sell gold for silver, then do not depart from him while there is a condition between you and him, except for 'take and give' (hand-to-hand)."