Musannaf Ibn Abi Shayba 13:2359

Abu Bakr narrated to us, he said: Shu'bah narrated to us, from Muhammad ibn Abi al-Mujalid, he said: Abu Burdah and Abdullah ibn Shaddad differed regarding the *salam* (forward sale), so they sent me to Ibn Abi Awfa. I asked him, and he said: "We used to engage in *salam* for wheat, barley, and raisins during the time of the Prophet, may Allah bless him and grant him peace, and Abu Bakr, and we do not know if any of his companions had anything against it or not."