Sahih Bukhari

Narrated Abu Wail from Hudhaifa:`Umar asked the people, ""Who remembers the narration of the Prophet (ﷺ) about the affliction?"" Hudhaifa said, ""I heard the Prophet (ﷺ) saying, 'The affliction of a person in his property, family and neighbors is expiated by his prayers, fasting, and giving in charity."" `Umar said, ""I do not ask about that, but I ask about those afflictions which will spread like the waves of the sea."" Hudhaifa replied, ""There is a closed gate in front of those afflictions."" `Umar asked, ""Will that gate be opened or broken?"" He replied, ""It will be broken."" `Umar said, ""Then the gate will not be closed again till the Day of Resurrection."" We said to Masruq, ""Would you ask Hudhaifa whether `Umar knew what that gate symbolized?"" He asked him and he replied ""He (`Umar) knew it as one knows that there will be night before tomorrow, morning