Sunan Ibn Majah, Chapter: The Chapters on Tribulations

"We were sitting with Umar and he said: 'Which of you has remembered a Hadith from the Messenger of Allah (saw) concerning Fitnah?'" Hudhaifah said: "I said: 'I have.' He said: 'You are very bold.' He said: 'How?' He said: 'I heard him say: "The fitnah of a man with regard to his family, his children and his neigbors are expiated by his prayers, fasts, charity and enjoining what is good and forbidding what is evil." Umar said: 'This is not what I meant, rather I meant that which moves like the waves of the sea.'" Hudhaifah said: "Don't worry about it, O Commander of the Believers! For there is a closed door between you and them." Umar said: "Will that door be broken or opened?" I said: "No, it will be broken." Umar said: "Then it will never be closed.'" We asked Hudhaifah: "Did Umar know what that door meant?" He said: "Yes, just as he knows that there will be night before morning, because I narrated to him a Hadith in which there are no errors." We were afraid to ask him who the door was, so we said to Masruq: "Ask him." He said: "Umar."