It was narrated from Ibn 'Abbas: "The Prophet (ﷺ) 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."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَإِسْحَاقُ بْنُ مَنْصُورٍ، قَالاَ حَدَّثَنَا يَزِيدُ بْنُ هَارُونَ، أَنْبَأَنَا مُسْتَلِمُ بْنُ سَعِيدٍ، عَنْ أَبِي عَلِيٍّ الرَّحَبِيِّ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ اغْتَسَلَ مِنْ جَنَابَةٍ فَرَأَى لُمْعَةً لَمْ يُصِبْهَا الْمَاءُ فَقَالَ بِجُمَّتِهِ فَبَلَّهَا عَلَيْهَا . قَالَ إِسْحَاقُ فِي حَدِيثِهِ فَعَصَرَ شَعْرَهُ عَلَيْهَا .
sunnah.com