Musnad Abu Ya'la al-Mawsili 115:326

Abu Musa narrated to us, Ibn Abi Adi narrated to us, from Sa’id, from Qatadah, from Anas, that the Prophet (peace and blessings of Allah be upon him) used to sacrifice two white-and-black-colored, horned rams. He would place his foot on their sides, slaughter them with his own hand, and say: "In the name of Allah, and Allah is the Greatest."