It is reported that Qatādah – Allāh have mercy on him – said:

Verily the Qurān guides you to your disease and your treatment: as for your disease, it is your sins; and as for your treatment, it is to seek the forgiveness of Allāh.

Al-Bayhaqī, Shuʿab Al-Īmān 9:347 no. 6745.