Musnad Ahmad 32:1478

Abu Salamah Yusuf ibn Ya'qub al-Majishun narrated to us, from Ibn Shihab, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) visited us in our house. We milked a domestic animal of ours for him, and we mixed its milk with water from the house. To the right of the Messenger of Allah (peace and blessings of Allah be upon him) was a man from the Bedouins, and behind that man was Umar ibn al-Khattab. To the left of the Messenger of Allah (peace and blessings of Allah be upon him) was Abu Bakr. The Messenger of Allah (peace and blessings of Allah be upon him) drank, and when he removed the vessel from his mouth, or intended to remove it, Umar said to him: "O Messenger of Allah, give it to Abu Bakr." But the Messenger of Allah (peace and blessings of Allah be upon him) gave the vessel to the Bedouin, then said: "The one on the right, then the one on the right."