The Messenger of Allah ﷺ said, "Change the gray hair, and do not imitate the Jews or the Christians."
حدثنا يزيد وابن نمير قالا حدثنا محمد بن عمرو عن أبي سلمة
قال رسول الله ﷺ غيروا الشيب ولا تشبهوا باليهود ولا بالنصارى
Its chain of transmission is sahih, and its meaning has already appeared in similar form at 7272 and 7533. As for this exact wording, Suyuti mentioned it in Jami Saghir 5785, attributing it to Musnad and Sahih Ibn Hibban.