Abu Rafi' (may Allah be pleased with him), the freed slave of the Messenger of Allah (peace and blessings be upon him), said: When the Messenger of Allah (peace and blessings be upon him) offered a sacrifice, he would buy two fat, piebald, horned rams. When he had finished the prayer and the sermon, he (peace and blessings be upon him) slaughtered one himself with a short spear and said: "This is on behalf of my entire Ummah, those who affirm Your Oneness and testify to my having conveyed (the message)." Then he slaughtered the other sacrifice and said: "O Allah, this is on behalf of Muhammad and the family of Muhammad." Then he would feed (of it) himself, his family and the poor. We remained for years, Allah having spared (us) the burden and the expense through the Messenger of Allah (peace and blessings be upon him), and none of Banu Hashim offered a sacrifice.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19049