حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا حَمَّادٌ، أَخْبَرَنَا عَطَاءُ بْنُ السَّائِبِ، عَنْ زَاذَانَ، عَنْ عَلِيٍّ، - رضى الله عنه - أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ مَنْ تَرَكَ مَوْضِعَ شَعْرَةٍ مِنْ جَنَابَةٍ لَمْ يَغْسِلْهَا فُعِلَ بِهِ كَذَا وَكَذَا مِنَ النَّارِ ‏"‏ ‏.‏ قَالَ عَلِيٌّ فَمِنْ ثَمَّ عَادَيْتُ رَأْسِي فَمِنْ ثَمَّ عَادَيْتُ رَأْسِي ثَلاَثًا ‏.‏ وَكَانَ يَجِزُّ شَعْرَهُ ‏.‏

Narrated Ali ibn AbuTalib: The Messenger of Allah (PBUH) said: If anyone who is sexual defiled leaves a spot equal to the breadth of a hair without washing, such and such an amount of Hell-fire will have to be suffered for it. Ali said: On that account I treated my head (hair) as an enemy, meaning I cut my hair. He used to cut the hair (of his head). May Allah be pleased with him. Translation Not Available

Book Ref: Sunan Abi Dawud Book 1 Hadith 249
Web Ref:  Sunan Abi Dawud Book 1 Hadith 249