Musannaf Ibn Abi Shaybah 21266 — A man who witnesses food being

Muhammad bin Sirin was asked about a man who bought grain while another was with him. The other says: "I have witnessed the sale and the taking of possession," and then wants to buy it at a profit to the first: may he buy it by that same measure? He said: It must be measured again before it is sold the second time, so that any surplus is his and any shortfall falls on him.