From Sahih Bukhari (Hadith 5656):
Narrated Ibn `Abbas:The Prophet (ﷺ) went to visit a sick bedouin. Whenever the Prophet (ﷺ) went to a patient, he used to say to him, "Don't worry, if Allah will, it will be expiation (for your sins):" The bedouin said, "You say expiation? No, it is but a fever that is boiling or harassing an old man and will lead him to his grave without his will." The Prophet (ﷺ) said, "Then, yes, it is so
Reference: Bukhari 5656