Musnad Abu Ya'la al-Mawsili 118:29

Wahb ibn Baqiyyah al-Wasiti narrated to us, Khalid narrated to us, from Abd al-Rahman ibn Ishaq, from al-Zuhri, from Anas, who said: I saw the Messenger of Allah (peace and blessings of Allah be upon him) drinking, and to his left was Abu Bakr, and to his right was a man from the Bedouins. He gave the remainder [of the drink] to the Bedouin, then said: "The one on the right, then the one on the right."