It was narrated that Abu Hurairah said: The Messenger of Allah said: 'Under every hair there is the state of sexual impurity, so wash the hair and cleanse the skin.'
Abu Ayyub Al-Ansari narrated that: The Prophet said: The five daily prayers, from one Friday to the next, and fulfilling the trust are all expiation for whatever (sins) come between them. I said: What is fulfilling the trust? He said: Having a bath to cleanse oneself from sexual impurity, for under every hair there is the state of sexual impurity.
It was narrated from 'Ali bin Abu Talib that: The Prophet said: Whoever leaves an area the size of a hair on his body and does not cleanse it from sexual impurity, such and such will be done to him in the Fire. 'Ali said: Because of that I am hostile towards my hair, and he used to shave his head.