Abd al-Rahman bin Jabir narrates from his father, Sayyiduna Jabir bin Abdullah (may Allah be pleased with him), that two piebald, horned, large, castrated rams were brought to the Prophet (peace and blessings be upon him). He laid one of them down and said while slaughtering: 'Bismillahi wallahu akbar' (In the name of Allah, and Allah is the Greatest). "O Allah, this is on behalf of Muhammad (peace and blessings be upon him)." Then, while slaughtering the other, he said: "O Allah, this is on behalf of Muhammad (peace and blessings be upon him) and the Ummah, those who affirmed Your Oneness and testified to the Prophet (peace and blessings be upon him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19048