Sahih Muslim Book 21, Hadith Number 4805.

Chapter : It is permissible to make use of things necessary for hunting and chasing but the use of small pebbles is disapproved.

Ibn Buraida reported that Abdullah b. al-Mughaffal saw a person from amongst his companions throwing small pebbles, whereupon he said: Don’t throw pebbles for Allah’s Messenger (may peace be upon him) did not like it, or he forbade flinging of pebbles since neither the game is taken thereby, nor an enemy defeated, but it may break a tooth or put out an eye. He, afterwards, again saw him flinging pebbles, and said to him: I inform you that the Messenger of Allah (may peace be upon him) did not approve or he forbade flinging of pebbles, but if I see you again flinging pebbles. I will not speak with you.