Musannaf Ibn Abi Shayba 16:77

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah narrated to us, from Ibrahim ibn Maysarah and Ibn Tawus, from his father, who said: The Prophet, peace and blessings of Allah be upon him, was asked about the *fara’* (the firstborn offspring of a camel or sheep sacrificed by the pre-Islamic Arabs). He said: "Sacrifice it if you wish. But that you feed it until it grows, then you carry upon it in the way of Allah, or you join kinship with it, is better than that you slaughter it, so its meat becomes mixed with its hair."