Sunan Ibn Majah, Book 32, Hadith 3765 (In-Book) ⓘ
It was narrated that Anas said: “The hair of the Messenger of Allah was wavy, and (hung down) between his ears and his shoulders.”
يَزِيدُ بْنُ هَارُونَ، أَنْبَأَنَا جَرِيرُ بْنُ حَازِمٍ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، قَالَ كَانَ شَعَرُ رَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ شَعَرًا رَجِلاً بَيْنَ أُذُنَيْهِ وَمَنْكِبَيْهِ.
also referenced under: Hadith 3634 (Reference) & Volume 4, Book 32, Hadith 3634 (DarusSalam)