The People of the Book used to let their hair hang down over their foreheads, while the polytheists parted their hair. The Messenger of Allah ﷺ liked to conform to the People of the Book in matters about which he had received no command, so at first he let his forelock hang down, but later he parted his hair.
و حدثني أبو الطاهر أخبرنا ابن وهب أخبرني يونس عن ابن شهاب بهذا الإسناد نحوه