(23) باب صِفَةِ النَّبِيِّ صلى الله عليه وسلم
Narrated Ibn `Abbas:
Allah's Messenger (ﷺ) used to let his hair hang down while the infidels used to part their hair. The people of the Scriptures were used to letting their hair hang down and Allah's Messenger (ﷺ) liked to follow the people of the Scriptures in the matters about which he was not instructed otherwise. Then Allah's Messenger (ﷺ) parted his hair.
Reference: Sahih al-Bukhari 3558
In-book reference: Book 61, Hadith 67
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 56, Hadith 758