Musannaf Ibn Abi Shayba 6:29

Abu Bakr ibn Ayyash narrated to us, from Asim, from Mus'ab ibn Sa'd, from his father, who said: I said, "O Messenger of Allah, which of the people are most severely tested?" He said, "The prophets, then those who are most like them, and then those who are most like them." "And the trial will continue to afflict the servant until he meets Allah while there is no sin upon him."