Full Sharh — Sunan Ibn Majah 664
حَدَّثَنَا سُوَيْدُ بْنُ سَعِيدٍ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ مُحَمَّدِ بْنِ عُبَيْدِ اللَّهِ، عَنِ الْحَسَنِ بْنِ سَعْدٍ، عَنْ أَبِيهِ، عَنْ عَلِيٍّ، قَالَ جَاءَ رَجُلٌ إِلَى النَّبِيِّ ـ صلى الله عليه وسلم ـ فَقَالَ إِنِّي اغْتَسَلْتُ مِنَ الْجَنَابَةِ وَصَلَّيْتُ الْفَجْرَ ثُمَّ أَصْبَحْتُ فَرَأَيْتُ قَدْرَ مَوْضِعِ الظُّفْرِ لَمْ يُصِبْهُ الْمَاءُ . فَقَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " لَوْ كُنْتَ مَسَحْتَ عَلَيْهِ بِيَدِكَ أَجْزَأَكَ " .
English Translation
It was narrated that 'Ali said:"A man came to the Prophet and said: 'I bathed to cleanse myself from sexual impurity, and I prayed Fajr, then I noticed a spot the size of a fingernail that the water did not reach.' The Messenger of Allah said: 'If you had wiped it that would have been sufficient for you
Source
Sunan Ibn Majah(سنن ابن ماجه)
The Book of Purification and its Sunnah
Hadith Number
664
Grade
Very Daif