ENOfficial
Thabit reported that Anas b. Malik was asked about the dyeing (of the hair of) Allah's Messenger (ﷺ). 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.
Source: sunnah.com
Other translations
Arabic
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 .
sunnah.com