Silsilah Sahihah

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Allah Almighty said: When I test My believing servant and he does not complain about Me to those who visit him, then I free him from My confinement, grant him better flesh in place of his former flesh, likewise give him better blood in place of his former blood, and he resumes his deeds anew."

Sayyiduna Abu Hurairah (may Allah be pleased with him) says: Umm Abdullah bint Abu Dhibab was ill, so I went to her to visit her. She said: O Abu Hurairah! Once I went to visit Sayyidah Umm Salamah (may Allah be pleased with her), who was sick. She saw a boil on my hand and said that I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "When Allah the Exalted tests a servant and he dislikes it due to his condition and state, then Allah the Exalted makes that hardship an expiation for his sins and a means of purifying him, as long as he does not present it at the door of anyone other than Allah (for cure) or call upon anyone other than Allah to remove it."