Sacrifice (Kitab Al-Dahaya)
Dawud :: Book 15 : Hadith 2782
Narrated Mikhnaf ibn Sulaym:
We were staying with the Apostle of Allah (peace_be_upon_him) at Arafat; he said: O people, every family must offer a sacrifice and an atirah. Do you know what the atirah is? It is what you call the Rajab sacrifice.