That the Messenger of Allah ﷺ said: "Whoever develops some gray hair in the cause of Allah, it shall be a light for him in the Day of Judgement.
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ مَنْ شَابَ شَيْبَةً فِي سَبِيلِ اللَّهِ كَانَتْ لَهُ نُورًا يَوْمَ الْقِيَامَةِ