Messenger of Allah ﷺ said, "The Jews and the Christians do not dye (their grey hair), so you shall do the opposite of what they do (i.e. dye your grey hair and beards).  

إِنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ الْيَهُودَ وَالنَّصَارَى لاَ يَصْبُغُونَ فَخَالِفُوهُمْ