Musnad Abu Ya'la al-Mawsili 115:235

Yahya ibn Ayyub narrated to us, Hushaym narrated to us, Shu'bah informed us, from Qatadah, from Anas, that the Messenger of Allah (may Allah bless him and grant him peace) used to sacrifice two white-and-black rams, and he would mention the name of Allah and say the takbir. He said: And I indeed saw him slaughtering them with his own hand, placing his foot upon their sides.