Musnad Ahmad 771:21

Yazid ibn Harun narrated to us, Salam ibn Miskin informed us, from 'Aidh Allah al-Mujashi'i, from Abu Dawud, from Zayd ibn Arqam, who said: I said, or they said: "O Messenger of Allah, what are these sacrificial animals?" He said: "The Sunnah of your father Ibrahim." They said: "What is there for us in them?" He said: "For every hair, a good deed." They said: "O Messenger of Allah, what about the wool?" He said: "For every hair of the wool, a good deed."