Musnad Abu Ya'la al-Mawsili 159:110

Ubayd Allah ibn Umar al-Qawariri narrated to us, Muslim ibn Khalid narrated to us, from Zayd ibn Aslam, from Ata ibn Yasar, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When you enter upon your Muslim brother, eat from his food and do not ask him [about it], and drink from his drink and do not ask him [about it]."