Mus'ab bin Sa'd narrates from his father: He said, "O Messenger of Allah (peace be upon him)! Who faces the most severe trials?" The Prophet (peace be upon him) said: "The Prophets, then those closest to them (in righteousness), then those closest to them. A person is tested according to the strength of his religion, and the trial continues to be with the servant until he walks upon the earth having no sin left upon him."