Jami` at-Tirmidhi 2398

Mus'ab bin Sa'd narrated from his father that a man said:"O Messenger of Allah(s.a.w)! Which of the people is tried most severely?" He said: "The Prophets, then those nearest to them, then those nearest to them. A man is tried according to his religion; if he is firm in his religion, then his trials are more severe, and if he is frail in his religion, then he is tried according to the strength of his religion. The servant shall continue to be tried until he is left walking upon the earth without any sins