The Messenger of Allah ﷺ said, "The best things to use for changing this gray hair are henna and katam."
قال رسول الله ﷺ: إن أحسن ما غير به هذا الشيب الحناء والكتم.
Reported by Abu Dawud (4205), Tirmidhi (1753), Nasai (5078), Ibn Majah (3622), and Ahmad (21307), and Ibn Hibban graded it sahih (5474), all of them through routes going back to Abdullah bin Burayda Aslami, from Abu Aswad, from Abu Dharr, who said what has been mentioned. Its chain of transmission is sahih. Tirmidhi said, "This is a hasan sahih hadith, and Abu Aswad Dili's name is Zalim bin Amr bin Sufyan."