AsalamAliukum! I want to ask a question. It is common in Pakistan and India that any disease can be cured by reciting Surah Rahman. I have searched for hadith or any authentic reference, but I am not able to find any authentic source. So I want to know that can Surah Rahman cure diseases/illnesses?
The Prophet Muhammad (صلي الله عليه وسلم) always had encouraged us to take treatments to help sustain life and our well being. He also mentioned that with every disease there is a treatment and Shifa.
So If there is a treatment for an illness/ disease then you must use that treatment. Also with alongside the treatment you can recite verses of the Quran or Ruqya for healing (Shifa). I have not come across any specific virtue that Surah Rahman cures diseases. However, saying this you can recite Surah Rahman and other Surah and verses with the intention of healing based on the verse below.