Sahih al-Bukhari, Hadith 5895 ⓘ
Narrated Thabit: Anas was asked whether the Prophet used a a hair dye or not. He replied, "The Prophet did not have enough grey hair to dye, (such that) if I wanted to count the fading hairs in his beard (I could have)."
حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ ثَابِتٍ، قَالَ سُئِلَ أَنَسٌ عَنْ خِضَابِ النَّبِيِّ، صلى الله عليه وسلم فَقَالَ إِنَّهُ لَمْ يَبْلُغْ مَا يَخْضِبُ، لَوْ شِئْتُ أَنْ أَعُدَّ شَمَطَاتِهِ فِي لِحْيَتِهِ.
also referenced under: Book 77, Hadith 112 (In-Book) & Volume 7, Book 72, Hadith 783 (USC-MSA)