Musnad Abu Ya'la al-Mawsili 118:26

And it was narrated to us again: Miskin ibn Bukayr narrated to us, from al-Awza'i, from Ibn Shihab, from Anas, that the Prophet (peace and blessings of Allah be upon him) drank while standing, and to his right was a Bedouin, and to his left was Abu Bakr. He gave it to the Bedouin and said, "The one on the right, then the one on the right."