What is the ruling on returning the money to a patient if they are not cured, when the doctor committed to that?

It is permissible to agree with a doctor for treatment in exchange for obtaining a cure. This is considered a form of ju'alah (stipulated payment for a task) and not ijarah (lease/hire) according to the majority of Maliki, Shafi'i, and Hanbali scholars. Evidence for this is drawn from the hadith of Abu Sa'id Al-Khudri regarding ruqyah (exorcism/spiritual healing) and receiving a payment for it. The Zahiris and Hanafis, however, prohibit this.