The Messenger of Allah ﷺ used to sacrifice goat out of every fifty goats. Abu Dawud said: Fara' means the first baby camel born (to the Arabs). They used to sacrifice it for their idols, and then eat it, and its skin was thrown on a tree. 'Atira was a sacrifice made during the first ten days of Rajab.
أَمَرَنَا رَسُولُ اللَّهِ ﷺ مِنْ كُلِّ خَمْسِينَ شَاةً شَاةٌ