What is the ruling on one who unjustly kills a non-believing person?

Taking a life, which Allah has forbidden, is one of the gravest sins. The Quran explicitly states the sanctity of life, except in truth, and that whoever kills a soul without cause—unless it be for murder or corruption in the land—it is as though he has killed all mankind. A peaceful disbeliever's life and property are inviolable, and it is not permissible to transgress against him if he is under a covenant or a pledge of security. It is reported in the Hadith (definition) that "whoever kills a person with whom he has a treaty will not smell the fragrance of Paradise." Islam has forbidden aggression against animals without reason, so how much more so against a human being whom Allah has honored? Scholars have differed regarding the ruling on retaliatory punishment (qisas) for a Muslim who intentionally kills a dhimmi (non-Muslim subject) disbeliever. The majority of scholars hold that a Muslim is not to be killed for a disbeliever, but rather is liable for blood money (diyah) if the disbeliever was not a combatant.