Musannaf Ibn Abi Shayba 13:59

Hafs and Ibn Fudayl narrated to us, from al-A’mash, from Ibrahim, that he saw no harm in [taking] collateral in a *salam* (forward sale) transaction. He said: It was said to him, "Sa’id ibn Jubayr says that is guaranteed profit." He said: "He takes the collateral, then the price rises."