(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).  

عَنْ أَنَسٍ خَادِمِ النَّبِيِّ ﷺ قَالَ قَدِمَ النَّبِيُّ ﷺ وَلَيْسَ فِي أَصْحَابِهِ أَشْمَطُ غَيْرَ أَبِي بَكْرٍ فَغَلَفَهَا بِالْحِنَّاءِ وَالْكَتَمِ  

"When the Prophet ﷺ arrived at Medina, the eldest amongst his companions was Abu Bakr. He dyed his hair with Hinna and Katam till it became of dark red color.  

قَدِمَ النَّبِيُّ ﷺ الْمَدِينَةَ فَكَانَ أَسَنَّ أَصْحَابِهِ أَبُو بَكْرٍ فَغَلَفَهَا بِالْحِنَّاءِ وَالْكَتَمِ حَتَّى قَنَأَ لَوْنُهَا