Musannaf Ibn Abi Shayba 13:2086

Abu Bakr narrated to us, he said: Hammad bin Khalid narrated to us, from Aflah, who said: I said to Al-Qasim: "A man requests wheat and oil from me, and I do not have it, except that he has known its price and I have known it, and I have bought it, then I sell it to him for a deferred term." He said: "Yes."