Musannaf Ibn Abi Shayba 16:75

Abu Bakr narrated to us, he said: Abdullah bin Numayr narrated to us, he said: Dawud bin Qays narrated to us, he said: Amr bin Shu’ayb narrated to me, from his father, from his grandfather, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was asked about the *Fara’* (the firstborn offspring of livestock). He said: "The *Fara’* is a right (i.e., it is a reality), but for you to leave it until it becomes a *Shifri* (a young camel) that is a *bint makhad* (one-year-old) or a *bint labun* (two-year-old), then you carry upon it in the path of Allah, or you give it to a widow, is better than that you slaughter it, so its meat sticks to its fur, you overturn your vessel, and you lose your she-camel." He was asked about the *‘Atirah* (a sacrifice performed in the month of Rajab), and the Messenger of Allah (peace and blessings of Allah be upon him) remained silent. Then some of the people asked Umar about the *‘Atirah*. He said: "We used to call it the *Rajabiyyah*. The people of a household would slaughter a sheep in Rajab and eat it."