Musannaf Ibn Abi Shayba 13:1137

Abu Bakr narrated to us, he said: Mu'tamir ibn Sulayman narrated to us, from Salam ibn Abi al-Dhayyal, who said: I asked Ibn Sirin about the one who sells goods in containers, when they have established between themselves a known weight for the containers. He said: He should sell it all by weight, with the containers included.