Sahih Muslim 144a

Muhammad ibn 'Abdullah ibn Numayr narrated to us: Abu Khalid—meaning Sulayman ibn Hayyan—narrated to us, from Sa'd ibn Tariq, from Rib'i, from Hudhayfa, who said: We were with 'Umar when he asked: Which of you has heard the Messenger of Allah (peace and blessings be upon him) speak about the trials? Some people said: We have heard him. He said: Perhaps you mean a man's trials with his family and neighbor. They said: Yes. He said: Prayer, fasting, and charity atone for those. But which of you has heard the Prophet (peace and blessings be upon him) speak about trials that surge like the waves of the sea? Hudhayfa said: The people fell silent, so I said: I have. He said: Well done! Hudhayfa said: I heard the Messenger of Allah (peace and blessings be upon him) say: Trials are presented to hearts like a reed mat is woven, strand by strand. Any heart that absorbs them receives a black spot, and any heart that rejects them receives a white spot, until there are two kinds of hearts: one white, like a smooth stone, which no trial will harm as long as the heavens and earth endure; the other black and dust-gray, like an overturned vessel, recognizing no good and rejecting no evil, except what its own desire has instilled in it. Hudhayfa said: I told him that between him and those trials was a closed door that was about to be broken. 'Umar said: Broken, you say? May your father be bereft of you! If it were merely opened, it might be closed again. I said: No, it will be broken. I told him that the door represented a man who would be killed or die. This is a report free of confusion. Abu Khalid said: I asked Sa'd, Abu Malik, what does black and dust-gray mean? He replied: An intense whiteness within blackness. I asked: What does an overturned vessel mean? He replied: Turned upside down.