Abu Dawud Book 9, Hadith Number 2827.
Chapter : The atirah.
Narated By ‘Aisha : The Apostle of Allah (PBUH) used to sacrifice a goat out of every fifty goats.
Abu Dawud said: Fara’ means the first baby of a camel born (to the Arabs). They used to sacrifice it for their idols, and then eat it, its skin was thrown on a tree. ‘Atriah was a sacrifice made during the first ten days of Rajab.