"The Prophet bathed to cleanse himself from sexual impurity, then he saw a spot that the water did not reach." Then he motioned with the hair hanging over his shoulders and squeezed (the water from it) over that spot." (Da'if)In his narration, Ishaq said: "So he wrung his hair over it."  

أَنَّ النَّبِيَّ ﷺ اغْتَسَلَ مِنْ جَنَابَةٍ فَرَأَى لُمْعَةً لَمْ يُصِبْهَا الْمَاءُ فَقَالَ بِجُمَّتِهِ فَبَلَّهَا عَلَيْهَا قَالَ إِسْحَاقُ فِي حَدِيثِهِ فَعَصَرَ شَعْرَهُ عَلَيْهَا  

"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.'"  

جَاءَ رَجُلٌ إِلَى النَّبِيِّ ﷺ فَقَالَ إِنِّي اغْتَسَلْتُ مِنَ الْجَنَابَةِ وَصَلَّيْتُ الْفَجْرَ ثُمَّ أَصْبَحْتُ فَرَأَيْتُ قَدْرَ مَوْضِعِ الظُّفْرِ لَمْ يُصِبْهُ الْمَاءُ فَقَالَ رَسُولُ اللَّهِ ﷺ لَوْ كُنْتَ مَسَحْتَ عَلَيْهِ بِيَدِكَ أَجْزَأَكَ