Sayyiduna Mikhnaf bin Sulaym (may Allah be pleased with him) said: We were standing with the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "O people! Indeed, upon every household, every year, a sacrifice and an 'atirah are obligatory. Do you know what the 'atirah is? It is the one that people call the Rajabiyyah."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17870