Musnad Abu Ya'la al-Mawsili 115:133

Abu Khaythama narrated to us, Ismail bin Ibrahim narrated to us, from Sa'id, from Qatada, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to sacrifice two white-and-black rams with horns. He would place his foot upon their sides, slaughter them with his own hand, and mention the name of Allah and say the takbir.