Sahih Muslim Book 002, Hadith Number 0505.
Chapter : How to cleanse oneself after relieving oneself.
Salman said that (one among) the polytheists remarked: I see that your friend even teaches you about the excrement. He replied; Yes, he has in fact forbidden us that anyone amongst us should cleanse himself with his right hand, or face the Qibla. He has forbidden the use of dung or bone for it, and he has also instructed us not to use less than three pebbles (for this purpose).