Musnad Ahmad 1494

Mus"ab bin Sa"d narrated that Sa"d said: I asked the Messenger of Allah (ﷺ): Which people are most severely tested? He said: "The Prophet (ﷺ), then the next best, then the next best. A man will be tested according to his level of religious commitment: if his religious commitment is weak, he will be tested according to that; if his religious commitment is solid, he will be tested in accordance with that." He said: "A man will be tested until he walks upon the face of the earth with not a single sin on him.”