Sahih Muslim 6062
صحيح مسلم#6062SahihIbn Abbas reported that the People of the Book used to let their hair fall (on their foreheads) and the polytheists used to part them on their heads, and Allah's Messenger (ﷺ) liked to conform his behaviour to the People of the Book in matters in which he received no command (from God) ; so Allah's Messenger (ﷺ) let fall his hair upon his forehead, and then he began to part it after this
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 43:120