Sayyiduna Anas bin Malik (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) sacrificed two horned black-and-white rams. I saw that he (peace and blessings be upon him) had placed his foot on their necks; then he said 'Bismillahi wallahu akbar' (In the name of Allah, and Allah is the Greatest) and slaughtered both of them with his own hands.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10221