Musnad Ahmad 32:1095

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was in our house, and a domestic sheep was milked for him. They mixed its milk with water from the house, then they handed it to the Prophet (peace and blessings of Allah be upon him). He drank, while Abu Bakr was to his left and a Bedouin was to his right. Umar said to him: "O Messenger of Allah, give it to Abu Bakr who is beside you," fearing that he would give it to the Bedouin. He said: So he gave it to the Bedouin, then he said: "The one on the right, then the one on the right."