Musannaf Ibn Abi Shayba 27:163

Affan narrated to us, he said: Hammad bin Salamah narrated to us, from Asim, from Zirr bin Hubaysh, from Abdullah bin Mas’ud, that he said: I was a young boy tending sheep for Uqbah bin Abi Mu’ayt. The Prophet (peace be upon him) and Abu Bakr came, having fled from the polytheists. They said: "O boy, do you have any milk to give us to drink?" I said: "I am a trustee, and I will not give you to drink." The Prophet (peace be upon him) said: "Do you have a young ewe that has not been mounted by a ram?" I said: "Yes." So I brought it to them. The Prophet (peace be upon him) restrained it, wiped the udder, and supplicated, and the udder filled. Then Abu Bakr brought him a hollowed or indented rock, and he milked into it. He drank, and Abu Bakr drank, then I drank. Then he said to the udder: "Shrink," and it shrank. He said: I came to him after that and said: "Teach me some of these words." He said: "You are a taught boy."