Musannaf Ibn Abi Shayba 16:203

Abu Bakr narrated to us, he said: Waki' narrated to us, from Sufyan, from 'Umar al-Ansari, he said: I heard Anas bin Malik saying: If you enter upon a man whom you do not suspect regarding his stomach (i.e., the source of his wealth), then eat from his food and drink from his drink.