From Sahih Bukhari (Hadith 5474):
Narrated Abu Huraira:The Prophet (ﷺ) said, "Neither Fara' nor 'Atira) is permissible)." Al-Fara' was the first offspring (they got of camels or sheep) which they (pagans) used to offer (as a sacrifice) to their idols. 'Atira was (a sheep which used to be slaughtered) during the month of Rajab
Reference: Bukhari 5474