Musnad Ahmad 834:34

Yazid narrated to us, Sa'id informed us, from Qatadah, from 'Uqbah ibn Sahban, from 'Abdullah ibn Mughaffal, from the Prophet, peace and blessings of Allah be upon him: That he forbade *al-khadhf* (flicking pebbles with the fingers), and he said: "It does not hunt game, and it does not injure an enemy, but it gouges out the eye and breaks the tooth." And Yazid said once: "It does not hunt game, and it does not injure an enemy."