Sunan an-Nasa'i, Book 48, Hadith 195 (In-Book) ⓘ
It was narrated from Anas that: The hair of the Prophet [SAW] came halfway down his ears.
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ أَنْبَأَنَا إِسْمَاعِيلُ، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، قَالَ كَانَ شَعْرُ النَّبِيِّ صلى الله عليه وسلم إِلَى نِصْفِ أُذُنَيْهِ .
also referenced under: Hadith 5234 (Reference) & Volume 6, Book 48, Hadith 5236 (DarusSalam)