Sahih Muslim Book 41, Hadith Number 6914.
Hudhaifa reported: We were one day in the company of ‘Umar that he said: Who amongst you has preserved in his mind most perfectly the hadith of Allah’s Messenger (may peace be upon him) in regard to the turmoil as he told about it? I said: It is I. Thereupon he said: You are bold (enough to make this claim). And he further said: How? I said: I heard Allah’s Messenger (may peace be upon him) as saying: There would (first) be turmoil for a person in regard to his family, his property, his own self, his children, his neighbours (and the sins committed in their connection) would be expiated by fasting, prayer, charity, enjoining good and prohibiting evil. Thereupon ‘Umar said: I do not mean (that turmoil on a small scale) but that one which would emerge like the mounting waves of the ocean. I said: Commander of the Faithful, you have nothing to do with it, for the door is closed between you and that. He said: Would that door be broken or opened? I said: No, it would be broken. Thereupon he said: Then it would not be closed despite best efforts. We said to Hudhaifa: Did Umar know the door? Thereupon he said: Yes, he knew it (for certain) just as one knows that night precede the next day. And I narrated to him something in which there was nothing fabricated. Shaqiq (one of the narrators) said: We dared not ask Hudhaifa about that door. So we requested Masrdq to ask him. So he asked him and he said: (By that door, he meant) ‘Umar.