Sahih Muslim 2341dBook 43, Hadith 134
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 .
(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.