Al-Adab Al-Mufrad #528

Ibn 'Abbas reported that the Prophet, may Allah bless him and grant him peace, went to visit a bedouin who was ill. When the Prophet, may Allah bless him and grant him peace, visited someone who was ill, he would say, 'There is no harm in it. It is a purification, Allah willing." That man then said, "A purification! No, rather it is a fever which boils (or appears) in an old man and will cause him to visit the graces." The Prophet, may Allah bless him and grant him peace, said, "Then yes (it is)".