Abu Dawud Book 1, Hadith Number 39.

Chapter : Things with which cleansing after easing oneself is forbidden.

Narated By Abdullah ibn Mas’ud : A deputation of the jinn came to the Prophet (PBUH) and said: O Muhammad, forbid your community to cleans themselves with a bone or dung or charcoal, for in them Allah has provided sustenance for us. So the Prophet (PBUH) forbade them to do so.