Sahih al-Bukhari 3919
Sahih al-Bukhari · Book 63: Merits of the Helpers in Madinah (Ansaar) · The emigration of the Prophet (saws) to Al-Madina
Narrated Anas:
حَدَّثَنَا سُلَيْمَانُ بْنُ عَبْدِ الرَّحْمَنِ ، حَدَّثَنَا مُحَمَّدُ بْنُ حِمْيَرَ ، حَدَّثَنَا إِبْرَاهِيمُ بْنُ أَبِي عَبْلَةَ ، أَنَّ عُقْبَةَ بْنَ وَسَّاجٍ ، حَدَّثَهُ عَنْ أَنَسٍ ، خَادِمِ النَّبِيِّ صلى الله عليه وسلم قَالَ قَدِمَ النَّبِيُّ صلى الله عليه وسلم وَلَيْسَ فِي أَصْحَابِهِ أَشْمَطُ غَيْرَ أَبِي بَكْرٍ، فَغَلَفَهَا بِالْحِنَّاءِ وَالْكَتَمِ .
(the servant of the Prophet) When the Prophet (ﷺ) arrived (at Medina), there was not a single companion of the Prophet (ﷺ) who had grey and black hair except Abu Bakr, and he dyed his hair with Henna' and Katam (i.e. plants used for dying hair).