Narrated Abu Hurairah (RAA):

Allah's Messenger (Peace be upon him) said: "There is Janabah (trace of sexual impurity) under every hair, so wash your hair and cleanse the skin." Abu Dawud and at-Tirmidhi transmitted it but they declared it to be weak.

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ إِنَّ تَحْتَ كُلِّ شَعْرَةٍ جَنَابَةً, فَاغْسِلُوا اَلشَّعْرَ, وَأَنْقُوا اَلْبَشَرَ } رَوَاهُ أَبُو دَاوُدَ, وَاَلتِّرْمِذِيُّ وَضَعَّفَاه ُ [1]‏ .‏