Sahih al-Bukhari 3550
Narrated Qatada:
I asked Anas, "Did the Prophet (ﷺ) use to dye (his) hair?" He said, "No, for there were only a few white 
hairs on his temples."
حَدَّثَنَا أَبُو نُعَيْمٍ، حَدَّثَنَا هَمَّامٌ، عَنْ قَتَادَةَ، قَالَ سَأَلْتُ أَنَسًا هَلْ خَضَبَ النَّبِيُّ صلى الله عليه وسلم قَالَ لاَ، إِنَّمَا كَانَ شَىْءٌ فِي صُدْغَيْهِ‏.‏