Musnad Abu Ya'la al-Mawsili 116:34

Ahmad narrated to us, Shababa narrated to us, Shu'bah narrated to us, from Qatadah, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) sacrificed two white-and-black rams with horns. And I saw him slaughtering them with his own hand, placing his foot upon their sides.