Musnad Abu Ya'la al-Mawsili 118:78

Narrated to us Wahb, informed us Khalid, from Abd al-Rahman, from al-Zuhri, from Anas, who said: I saw the Messenger of Allah (may Allah bless him and grant him peace) drink milk. To his left was Abu Bakr, and to his right was a man from the Bedouins. He gave the remainder to the Bedouin, then said: "The one on the right, then the one on the right."