Mukhtasar Bukhari (Abridged) 1949 — Expiation for illness

It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) and Abu Hurairah (may Allah be pleased with him) that the Noble Prophet (peace and blessings of Allah be upon him) used to say: "No hardship (or illness, sorrow, grief, or pain) befalls a Muslim except that Allah, in return, wipes out some of his sins because of it, even if a thorn pricks him (then in exchange for that too, some sin is wiped out)."