Musnad Ahmad 5:229

'Affan narrated to us, Hammam narrated to us, Qatadah narrated to us, a man from Banu Sadus, who is called Jurayy ibn Kulayb, narrated to us, from Ali ibn Abi Talib: "That the Prophet, peace and blessings of Allah be upon him, forbade the 'adba' (the ear that is slit or cut) and the horn." He said: So I asked Sa'id ibn al-Musayyib, and he said: "Half or more than that."