Musnad Ahmad 769:20

Hajjaj narrated to us, Shu'bah narrated to me, from Abu al-Mukhtar, from the tribe of Banu Asad, who said: I heard Abdullah ibn Abi Awfa say: We were on a journey and did not find water. He said: Then we came upon water afterward. He said: So they began to give the Messenger of Allah, peace and blessings of Allah be upon him, to drink. Every time they brought him the drink, the Messenger of Allah, peace and blessings of Allah be upon him, said: "The one who gives the people to drink is the last of them," three times, until they had all drunk.