Sahih Bukhari
Good Manners and Form (Al-Adab)
Volume: 008 / Book Number: 073 / Hadith Number: 239
Narrated 'Abdullah bin Mughaffal Al-Muzani:
The Prophet forbade the throwing of stones (with the thumb and the index or middle finger), and said "It neither hunts a game nor kills (or hurts) an enemy, but it gouges out an eye or breaks a tooth."