It is narrated from Sayyiduna Abu Umamah al-Bahili (may Allah be pleased with him) that the Prophet of Allah (peace and blessings be upon him) said: "There is no servant who is struck down by a bout of illness except that Allah raises him up from it purified."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7454