Sayyiduna Abdullah bin Mughaffal (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) forbade flicking pebbles and said: "Game cannot be hunted with it, nor can an enemy be harmed with it; rather, flicking pebbles will gouge out an eye or break a tooth."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيد والذبائح / 18944