What is the ruling on killing ambassadors of states that fight us, and what is the ruling on rejoicing over that and showing it?

Killing ambassadors of infidel nations—even if they are at war [with Muslims]—within Muslim lands is forbidden by Islamic law, and it is impermissible to rejoice over this forbidden act, as it is a disobedience to Allah. However, if one rejoices at his killing because it signifies freedom from his evil and deliverance of people from his oppression, and not because of joy in disobeying Allah, then there is no harm in that. If one does not know which of the two reasons his joy stems from, then there is no sin upon him, because the apparent reason is that he rejoices at the misfortune of his enemy for the sake of relief from him, not for the disobedience.