Narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) came to Umm Sa’ib or Umm Musayyib and asked: "Umm Sa’ib! What has happened to you? You are trembling." She replied: "It is fever, may Allah not bless it." The Prophet (peace and blessings of Allah be upon him) said: "Do not curse fever, for it removes the sins of the children of Adam just as a furnace removes the impurities of iron."

It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no (believing) servant who is laid low by illnesses, but when Allah, the Exalted, raises him up (by granting him recovery), he becomes purified."

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Noble Prophet (peace and blessings of Allah be upon him) said: "A believer is always tested in regard to his life, his children, and his wealth, until when he meets Allah Almighty, (because of these trials) his sins have been forgiven."

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 Lady Umm Salamah (may Allah be pleased with her), who was ill. She saw a boil on my hand and said that I heard the Messenger of Allah (peace and blessings be upon him) say: "When Allah Almighty tests a servant and he dislikes it because of his condition and state, Allah makes that hardship an expiation for his sins and a means of purification for him, as long as he does not present it at the door of anyone other than Allah (to seek a cure), nor does he call upon anyone other than Allah to remove it."

Sayyiduna Abu Burdah (may Allah be pleased with him) narrates from one of the wives of the Prophet (peace and blessings be upon him)—most likely it was Sayyidah Aisha (may Allah be pleased with her)—that the Messenger of Allah (peace and blessings be upon him) fell ill, and due to this illness, he experienced severe distress and pain. Sayyidah Aisha (may Allah be pleased with her) said:“O Messenger of Allah! You are anxious and restless; if I were to do this, you would be surprised at me.”The Prophet (peace and blessings be upon him) replied:“Do you not know that the hardship upon a believer is so that it may become an expiation for his sins?”

It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When a servant becomes ill, Allah Almighty commands the angels: O My angels! I have confined My servant in one of My (trials). If I cause him to die, I will forgive him, and if I grant him well-being (from this illness), he will sit (recovered) and there will be no sin upon him."

It is narrated from Sayyiduna Abdur Rahman bin Azhar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The example of a believing servant, when he is afflicted with fever, is like that of iron which is thrown into the fire; its impurities are removed and the useful part remains."

Sayyiduna Abu Hurairah (may Allah be pleased with him) says that I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Indeed, Allah the Exalted continues to test His servant through illnesses, until (these illnesses) become an expiation for all his sins."

It is narrated from Sayyidah Aisha (may Allah be pleased with her) that when the Messenger of Allah (peace and blessings be upon him) was afflicted with any pain, he would groan and turn from side to side. Sayyidah Aisha (may Allah be pleased with her) said: If any of us did this (because of pain), you would notice it (but you are doing it yourself). The Noble Prophet (peace and blessings be upon him) said:“(In matters of illness) righteous people are put to greater hardship, and even the pain of a thorn pricking a believer causes his sins to be forgiven and his rank to be elevated.”

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."