Musnad Ahmad 28:283

'Abd al-Razzaq narrated to us, Dawud ibn Qays informed us, I heard 'Amr ibn Shu'ayb narrating from his father, from 'Abdullah ibn 'Amr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was asked about the *Fara'* (the firstborn offspring of livestock sacrificed by the polytheists). He said: "The *Fara'* is a right (truth/reality). But if you leave it until it becomes a strong young camel, either a one-year-old (*ibn makhad*) or a two-year-old (*ibn labun*), and you carry upon it in the way of Allah, or you give it to a widow, that is better than slaughtering it, letting its flesh stick to its fur, overturning your vessel, and abandoning your she-camel."