Jaabir ibn `Abdullaah reported that the Messenger of Allah, sallallaahu ‘alayhi wa sallam, visited Umm As-Saa’ib (a woman Companion) and said to her: “What is the matter with you, O Umm As-Saa’ib, why are you shivering so violently?” She said: “I have a fever, may Allah not bless it!” The Prophet of Allah, sallallaahu ‘alayhi wa sallam, said: “Do not curse fevers, because they do away with the sins of the children of Adam just as a furnace does away with the impurities of iron.”
‘Abdullaah ibn ‘Abbaas (the Prophet’s cousin) said: “The Prophet of Allah, sallallaahu ‘alayhi wa sallam, visited a Bedouin who was sick. The Prophet
of Allah, sallallaahu ‘alayhi wa sallam, used to say when he visited a sick person,
‘Laa Ba’s, Tahoor In shaa’ Allah [No harm, it will be a purification (of
sins) if Allah wills].’ So he said that, and the Bedouin man said: ‘A purification! Rather, it is a fever that boils in an old man and takes him to the grave.’
The Prophet of Allah, sallallaahu ‘alayhi wa sallam, said: ‘Then yes, so it shall
be.’” In another narration the Prophet of Allah, sallallaahu ‘alayhi wa sallam, said: “The man did not live until the next evening.”