Hudhaifa reported: We were sitting with Umar ibn Al-Khatab and he said, “Who among you has heard the Messenger of Allah mention tribulation?” Some people said, “We have heard it.” Umar said, “Perhaps it is the unrest a man might experience with his household and neighbor.” They said yes. Umar said, “Such unrest will disappear with prayer, fasting, and charity. Rather, who has heard mention from the Prophet describing a tribulation like the waves of the ocean?” The people were silent and I said I have heard it. Umar said, “You and your father are good men for Allah.” I said I heard the Messenger of Allah, peace and blessings be upon him, say, “Tribulation will be presented to the hearts of people like a reed mat woven stick by stick and any heart afflicted by them will have a black mark put into it, but any heart that rejects them will have a white mark put into it. Thus there will be two kinds of hearts: one is pure like a white gemstone and it will not be harmed by any tribulation as long as the heavens and earth endure, and the other is black and dusty like a worn-out vessel, neither recognizing good nor rejecting evil, but rather immersed in its desires.” [Source: Sahih Muslim 144, Grade: Sahih (authentic) according to Muslim].