The Prophet ﷺ said, "Neither Fara' nor 'Atira (is permissible):" Al-Fara' nor 'Atira (is permissible):" Al- Fara' was the first offspring (of camels or sheep) which the pagans used to offer (as a sacrifice) to their idols. And Al-ʿAtira was (a sheep which was to be slaughtered) during the month of Rajab.  

عَنِ النَّبِيِّ ﷺ قَالَ لاَ فَرَعَ وَلاَ عَتِيرَةَ وَالْفَرَعُ أَوَّلُ النِّتَاجِ كَانُوا يَذْبَحُونَهُ لَطِوَاغِيتِهِمْ وَالْعَتِيرَةُ فِي رَجَبٍ