Musannaf Ibn Abi Shayba 13:546

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Muhammad ibn Sharik, from Ibn Abi Mulayka, who said: A man bought food from a man, some of which was in his possession and some of which was not in his possession. So he asked Ibn Abbas and Ibn ‘Amr. They said: "Whatever was in his possession is permissible, and whatever was not in his possession is nothing."