Musannaf Ibn Abi Shayba 16:68

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Ma’mar, from al-Zuhri, from Sa’id ibn al-Musayyib, from Abu Hurayrah, that the Prophet, may God bless him and grant him peace, said: "There is no *Fara’* and no *’Atirah*." Al-Zuhri said: As for the *Fara’*, it is the first offspring that they produce from their livestock, which they would slaughter for their idols. And the *’Atirah* is in Rajab.