Musnad Ahmad 5:592

Muhammad ibn Ja'far narrated to us, Sa'id narrated to us, from Qatadah, from Jurayy ibn Kulayb: That he heard Ali saying: "The Messenger of Allah, peace and blessings of Allah be upon him, forbade sacrificing an animal with a slit horn or ear." Qatadah said: I mentioned that to Sa'id ibn al-Musayyib, and he said: "Yes, the 'adhab' (slit) is half or more than that."