Abu Ali Sina, known in the West as Avicenna, was the foremost physician and philosopher of his time. His work, Al-Qanun fi’l-Tibb (The Canon of Medicine), is recognised as the most influential book in the history of medicine. He was the first to identify that diseases are spread by germs and to recognise the close connection between mental health and physical well-being. The basic concept of quarantine also stems from his work. In addition to medicine, he made outstanding contributions to physics and astronomy.
Reference: Al-Qanun fi’t-Tib, Ibn Sina: His Life and Contributions.