Sahih al-Bukhari, Book 77, Hadith 121 (In-Book) ⓘ
Narrated Anas: The head-hair of the Prophet used to hang down to his shoulders.
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا هَمَّامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، كَانَ يَضْرِبُ شَعَرُ النَّبِيِّ صلى الله عليه وسلم مَنْكِبَيْهِ.
also referenced under: Hadith 5904 (DarusSalam) & Volume 7, Book 72, Hadith 790 (USC-MSA)