Musnad Ahmad 5:502

'Abd al-Rahman ibn Mahdi narrated to us, Shu'bah narrated to us, from Qatadah, who said: I heard Jurayy ibn Kulayb narrating from 'Ali, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade the *'adhab* (slitting/cutting) of the ear and the horn." He said: So I asked Sa'id ibn al-Musayyib: "What is the *'adhab*?" He said: "Half [of it] or more than that."