Musnad Ahmad 834:1

Yahya ibn Sa'id narrated to us, from Shu'bah, and Muhammad ibn Ja'far, Shu'bah narrated to us, Qatadah narrated to us, from 'Uqbah ibn Sahban, from Ibn Mughaffal, that the Messenger of Allah (ﷺ) forbade *al-khadhf* (flicking pebbles with the fingers). He said: "It does not injure an enemy, nor does it hunt game, but it breaks the tooth and gouges out the eye."