Sayyiduna Mikhnaf bin Sulaym (may Allah be pleased with him) said: We stood at Arafah with the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) said: "Upon every household, every year, there is a sacrifice and an 'atirah. Do you know what the 'atirah is?" The narrator said: I do not know what they replied. Then he said: "It is what people call the Rajabiyyah, that is, an animal set aside to be slaughtered in the month of Rajab."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19010