Musannaf Ibn Abi Shayba 13:1468

Abu Bakr narrated to us, he said: Ali bin Mushir narrated to us, from Ubaydullah, from Nafi’, from Ibn Umar, who said: We used to meet the caravans and buy food from them by estimation (without weighing or measuring). The Messenger of Allah (peace and blessings of Allah be upon him) forbade us from selling it until we moved it from its place or transported it.