It is narrated from Sayyidah Aishah (may Allah be pleased with her) or Sayyiduna Abu Hurayrah (may Allah be pleased with him) (the doubt is Sufyan's) that when the Messenger of Allah (peace and blessings be upon him) intended to sacrifice, he would sacrifice two fat, black-and-white, horned and castrated rams: one sacrifice on behalf of his Ummah, whoever testified that he had conveyed (the message) and bore witness to the Oneness of Allah, and the other sacrifice on behalf of Muhammad (peace and blessings be upon him) and the family of Muhammad (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19088