The Book of Adornment
48/6. Chapter:
Cutting the (Hair)
Sunan an-Nasai
أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا وَهْبُ بْنُ جَرِيرٍ، قَالَ حَدَّثَنَا أَبِي قَالَ، سَمِعْتُ قَتَادَةَ، يُحَدِّثُ عَنْ أَنَسٍ، قَالَ كَانَ شَعْرُ النَّبِيِّ صلى الله عليه وسلم شَعْرًا رَجِلاً لَيْسَ بِالْجَعْدِ وَلاَ بِالسَّبْطِ بَيْنَ أُذُنَيْهِ وَعَاتِقِهِ .
It was narrated that Anas said: "The hair of the Prophet [SAW] was wavy, neither curly nor straight, and (hung down) between his ears and his shoulders."
Reference : Sunan an-Nasa'i 5053In-book reference : Book 48, Hadith 14English translation : Vol. 6, Book 48, Hadith 5056