حَدَّثَنَا عَفَّانُ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ أَخْبَرَنَا عَطَاءُ بْنُ السَّائِبِ عَنْ زَاذَانَ أَنَّ عَلِيَّ بْنَ أَبِي طَالِبٍ رَضِيَ اللَّهُ عَنْهُ قَالَ سَمِعْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ مَنْ تَرَكَ مَوْضِعَ شَعَرَةٍ مِنْ جَسَدِهِ مِنْ جَنَابَةٍ لَمْ يُصِبْهَا الْمَاءُ فُعِلَ بِهِ كَذَا وَكَذَا مِنْ النَّارِ قَالَ عَلِيٌّ رَضِيَ اللَّهُ عَنْهُ فَمِنْ ثَمَّ عَادَيْتُ رَأْسِي
مسند امام احمد بن حنبل · Hadith 794
It was narrated from Zadhan that 'Ali (RA) said: I heard the Prophet (PBUH) say: "Whoever leaves a space the size of a hair on his side when doing ghusl for janabah and does not make water reach it, Allah will punish him with such and such of fire." 'Ali (PBUH) said: From that time I disliked my head (i.e., hair).
Translated by Dr. Muhammad Muhsin Khan · Reviewed by Islamic University of Madinah · Published March 2020