Mus'ab bin Sa'd narrates from his father, Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him), that he said: I asked the Messenger of Allah (peace and blessings be upon him): Which people are most severely tried? He (peace and blessings be upon him) said: "The Prophets; then those next in rank, one degree after another. A man is tried according to his religion. If he is firm in religion, his trial is more severe; and if there is weakness in his religion, he is tried according to his religion. Trials keep befalling the servant until they leave him walking on the earth with no sin upon him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6534