Musannaf Ibn Abi Shayba 13:1463

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mughira, he said: I asked Ibrahim about a man who was [selling] by estimation (juzafan). He said to him: "Whatever is in your house of wheat, then it is for such-and-such, and whatever is of barley, then it is for such-and-such." He said: So Ibrahim disliked it.