Musnad Ahmad 30:2062

Husayn ibn Muhammad narrated to us, he said: Muslim—meaning Ibn Khalid—narrated to us, from Zayd ibn Aslam, from Sumayy, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If one of you enters upon his Muslim brother, and he feeds him food, then let him eat from his food, and let him not ask him about it. And if he gives him a drink from his drink, then let him drink from his drink, and let him not ask him about it."