What is the ruling on a private physician refusing to treat poor patients whose condition is critical due to their inability to pay, while justifying this by saying that he performs free operations and arguing that medical treatment is not obligatory?

A doctor is not obligated to perform free surgical operations to save patients' lives if someone else is available. However, if no one else is available to perform operations that would save their lives, then it becomes obligatory upon the doctor to do so. In such a case, the ruler (wali al-amr) must compel the doctor to treat them for a customary fee. This is based on the principle that actions which are a communal obligation (fard kifayah) become an individual obligation (fard ayn) if no one else performs them and people are in need of them.