From Sahih Bukhari (Hadith 5895):
Narrated Thabit:Anas was asked whether the Prophet (ﷺ) used a a hair dye or not. He replied, "The Prophet (ﷺ) did not have enough grey hair to dye, (such that) if I wanted to count the fading hairs in his beard (I could have)
Reference: Bukhari 5895