Mishkat al-Masabih 3 Purification كتاب الطهارة 153

وَعَن عَليّ قَالَ: جَاءَ رَجُلٌ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ إِنِّي اغْتَسَلْتُ مِنَ الْجَنَابَةِ وَصليت الْفجْر ثمَّ أَصبَحت فَرَأَيْتُ قَدْرَ مَوْضِعِ الظُّفُرِ لَمْ يُصِبْهُ الْمَاءُ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَوْ كُنْتَ مَسَحْتَ عَلَيْهِ بِيَدِكَ أَجْزَأَكَ» . رَوَاهُ ابْن مَاجَه

‘Ali reported that a man came to the Prophet and said, “I washed because of sexual defilement, then prayed the dawn prayer but noticed a spot about the size of a nail which had not been touched by the water.” God’s messenger replied, “If you had rubbed your hand over it, it would have been enough for you.” Ibn Majah transmitted it.