Sunan an-Nasa'i 5086
It was narrated from Qatadah :
That he asked Anas: "Did the Messenger of Allah [SAW] dye his hair? He said: "His gray hair didn't go far, it was only a little at his temples."
أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا أَبُو دَاوُدَ، قَالَ حَدَّثَنَا هَمَّامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، أَنَّهُ سَأَلَهُ هَلْ خَضَبَ رَسُولُ اللَّهِ صلى الله عليه وسلم قَالَ لَمْ يَبْلُغْ ذَلِكَ إِنَّمَا كَانَ شَىْءٌ فِي صُدْغَيْهِ ‏.‏