(14) باب مَا يُقَالُ لِلْمَرِيضِ وَمَا يُجِيبُ
Narrated Ibn `Abbas:
Allah's Messenger (ﷺ) entered upon sick man to pay him a visit, and said to him, "Don't worry, Allah willing, (your sickness will be) an expiation for your sins." The man said, "No, it is but a fever that is boiling within an old man and will send him to his grave." On that, the Prophet (ﷺ) said, "Then yes, it is so."
Reference: Sahih al-Bukhari 5662
In-book reference: Book 75, Hadith 23
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 7, Book 70, Hadith 566