It is related in a hadith that Rasulullah (Sallallahu alaihe wasallam) once came out of his house, wiping his hands on his blessed beared. Abu Bakr and Umar R.A. were sitting in the Masjid at that time. When AbuBakr R.A. saw this he said: 'O Messenger of Allah, may my father and mother be sacrificed for you. How early you have aged'. Then he began to weep. Rasulullah (Sallallahu alaihe wasallam) said: "Surahs like Surah Hud have made me old".Zamakh'shari says: "He read in a kitaab, that a person had pure black hair one evening, and during the night it became completely white. When the people enquired of this sudden change, he said: "At night, I saw Qiyaamah, in my dream. People were being pulled with chains and thrown into Hell. It frightened me so much, that within the night I became like this". Allah is Great.