Did the Muslim doctors find a treatment for smallpox?

The answer is: yes

The first individuals to inoculate against smallpox were Chinese doctors. Variolation, the inoculation of smallpox material into healthy individuals to induce immunity, was practiced in China as early as 1000 CE. The Chinese used two methods of inoculation: the dry or insufflation method and the wet method. Muslim physicians later adopted the technique and introduced it to the rest of the Islamic world and eventually Europe.