The Messenger of Allah ﷺ said, "Change the grey hair, and do not imitate the Jews or the Christians."
قال رسول الله ﷺ: غيروا الشيب، ولا تشبهوا باليهود ولا بالنصارى.
Tirmidhi (1752) and Ahmad (7545) narrated it, and Ibn Hibban (5473) graded it sahih, all of them through the route of Umar bin Abu Salama, from his father, from Abu Hurairah, who reported it. Some narrators were content to mention only the Jews. Its isnad is sahih. Tirmidhi said, "Hasan sahih."