Musnad Ahmad 2203

It was narrated that Ibn 'Abbas (رضي الله عنه) said: The mushrikeen used to part their hair in the middle and the People of the Book used to let their hair fall over their foreheads, and the Messenger of Allah (ﷺ) liked to do the same as the People of the Book - Ya'qoob said: in some matters concerning which he had received no command; Ishaq said: in that concerning which he had received no command - so he let his hair fall over his forehead, then later on he parted it.