حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا الْحَارِثُ بْنُ وَجِيهٍ، حَدَّثَنَا مَالِكُ بْنُ دِينَارٍ، عَنْ مُحَمَّدِ بْنِ سِيرِينَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏"‏ إِنَّ تَحْتَ كُلِّ شَعَرَةٍ جَنَابَةً فَاغْسِلُوا الشَّعَرَ وَأَنْقُوا الْبَشَرَةَ ‏"‏ ‏.‏

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.