Musnad Ahmad 57:2

Rawh narrated to us, Zakariya ibn Ishaq narrated to us, he said: 'Amr ibn Abi Sufyan narrated to me, he said: Muslim ibn Shu'bah narrated to me, that 'Alqamah appointed his father over the leadership of his people. Muslim said: My father sent me to a collector of charity among a group of my people. He said: So I went out until I came to an old man who was called Sa'r, in one of the mountain passes. I said: My father sent me to you so that you would give me the charity of your sheep. He said: O son of my brother, and which [type] do you take? I said: We take the best that we find. The old man said: I was in one of these mountain passes with sheep of mine, when two men came to me riding together on a camel. They said: We are the messengers of the Messenger of Allah (may Allah bless him and grant him peace); he sent us to you so that you would give us the charity of your sheep. I said: And what is it? They said: "A sheep." So I went to a sheep, the place of which I knew, full of pregnancy—or fat—and flesh, and I brought it out to them. They said: "This is a *shafi'*, and the Messenger of Allah (may Allah bless him and grant him peace) has forbidden us to take a *shafi'*"—and the *shafi'* is the one that has its offspring in its womb. He said: So I said, what thing do you take? They said: "A young female goat, or a one-year-old, or a two-year-old." He said: So I brought out a young female goat for them. He said: They said, hand it over to us. So they took it and placed it with them on their camel.