Sayyiduna Ibn Umar (may Allah be pleased with them both) narrated that Umar bin al-Khattab (may Allah be pleased with him) did not change (the colour of) his white hair. It was said to him: "O Commander of the Believers, why do you not dye it, when Abu Bakr (may Allah be pleased with him) used to dye his?" Umar (may Allah be pleased with him) said: "I heard the Messenger of Allah (peace and blessings be upon him) say: 'Whoever has a hair turn white in Islam, it will be a light for him on the Day of Resurrection.' And I will not change my white hair."
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 57