Musannaf Ibn Abi Shayba 13:1442

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Aslam al-Minqari, from Sa’id ibn Jubayr, regarding a man who enters into a *salam* (forward sale) contract, saying: "I have such-and-such amount of wheat with you for such-and-such price," or "I have such-and-such amount of grains with you for such-and-such price." He disliked it.