"The Messenger of Allah said: 'Under every hair there is the state of sexual impurity, so wash the hair and cleanse the skin.'"  

قَالَ رَسُولُ اللَّهِ ﷺ إِنَّ تَحْتَ كُلِّ شَعَرَةٍ جَنَابَةً فَاغْسِلُوا الشَّعَرَ وَأَنْقُوا الْبَشَرَةَ  

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."  

أَنَّ النَّبِيَّ ﷺ قَالَ الصَّلَوَاتُ الْخَمْسُ وَالْجُمُعَةُ إِلَى الْجُمُعَةِ وَأَدَاءُ الأَمَانَةِ كَفَّارَةٌ لِمَا بَيْنَهَا قُلْتُ وَمَا أَدَاءُ الأَمَانَةِ قَالَ غُسْلُ الْجَنَابَةِ فَإِنَّ تَحْتَ كُلِّ شَعَرَةٍ جَنَابَةً  

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.  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ تَرَكَ مَوْضِعَ شَعَرَةٍ مِنْ جَسَدِهِ مِنْ جَنَابَةٍ لَمْ يَغْسِلْهَا فُعِلَ بِهِ كَذَا وَكَذَا مِنَ النَّارِ قَالَ عَلِيٌّ فَمِنْ ثَمَّ عَادَيْتُ شَعَرِي وَكَانَ يَجُزُّهُ