Musnad Abu Ya'la al-Mawsili 126:9

'Abd al-A'la narrated to us, Khalid bin 'Abdullah narrated to us, from 'Abdullah bin 'Abd al-Rahman, from Anas bin Malik, who said: A sheep was milked for the Messenger of Allah (ﷺ), and its milk was brought to him. He called for water and poured it into the milk. He drank, and 'Umar was facing him, Abu Bakr was to his left, and a Bedouin was to his right. 'Umar said, "Abu Bakr is with you." He (the Prophet) said, "The ones on the right, the ones on the right." So he handed it to the Bedouin.