Sahih al-Bukhari 3550
Sahih al-Bukhari · Book 61: Virtues and Merits of the Prophet (pbuh) and his Companions · The description of the Prophet (saws)
Narrated Qatada:
حَدَّثَنَا أَبُو نُعَيْمٍ ، حَدَّثَنَا هَمَّامٌ ، عَنْ قَتَادَةَ ، قَالَ سَأَلْتُ أَنَسًا هَلْ خَضَبَ النَّبِيُّ صلى الله عليه وسلم قَالَ لاَ، إِنَّمَا كَانَ شَىْءٌ فِي صُدْغَيْهِ.
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."