حَدَّثَنِي أَبُو الرَّبِيعِ الْعَتَكِيُّ، حَدَّثَنَا حَمَّادٌ، حَدَّثَنَا ثَابِتٌ، قَالَ سُئِلَ أَنَسُ بْنُ مَالِكٍ عَنْ خِضَابِ النَّبِيِّ، صلى الله عليه وسلم فَقَالَ لَوْ شِئْتُ أَنْ أَعُدَّ شَمَطَاتٍ كُنَّ فِي رَأْسِهِ فَعَلْتُ ‏.‏ وَقَالَ لَمْ يَخْتَضِبْ وَقَدِ اخْتَضَبَ أَبُو بَكْرٍ بِالْحِنَّاءِ وَالْكَتَمِ وَاخْتَضَبَ عُمَرُ بِالْحِنَّاءِ بَحْتًا ‏.‏

Thabit reported that Anas b. Malik was asked about the dyeing (of the hair of) Allah's Apostle (PBUH). Thereupon he said.: (They were so few) that if I so liked I could count their number in his head, and he further said: (That is) he did not dye. Abu Bakr, however, dyed them and so did 'Umar dye them with pure henna. Translation Not Available

Book Ref: Sahih Muslim Book 43 Hadith 5782
Web Ref:  Sahih Muslim Book 30 Hadith 2341 d