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." Translation Not Available

Book Ref: Sunan An Nisai Book 48 Hadith 5053
Web Ref:  Sunan An Nisai Vol 6 Book 48 Hadith 5056