Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with the same chain of narration, it is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that milk mixed with (well) water was brought to the Messenger of Allah (peace and blessings be upon him). On his right was a Bedouin (villager) and on his left was Sayyiduna Abu Bakr Siddiq (may Allah be pleased with him). The Prophet (peace and blessings be upon him) drank (the milk), then gave (the remaining milk) to the Bedouin and said: "The right (has precedence), then (whoever is) on the right after him."

And with this same chain (it is narrated from Sayyiduna Sahl bin Sa’d, may Allah be pleased with him) that a drink (i.e., milk) was brought to the Prophet, peace and blessings be upon him, and he drank from it. On his right was a boy and on his left were elderly people, so he said to the boy: If you permit me, shall I give this (remaining portion) to these (elderly) people? The boy said: No, O Messenger of Allah! By Allah, I will not give preference to anyone over your leftover. So the Messenger of Allah, peace and blessings be upon him, placed it in his hand.