What is the ruling on slandering a male or female non-dhimmi or non-musta'min disbeliever, and what is the ruling on slandering a Muslim who has committed adultery and has not repented?

It is not permissible to harm a peaceful disbeliever, and slandering him is forbidden; the perpetrator is subject to disciplinary punishment (ta'zeer), but not the hadd punishment for slander. As for a Muslim who commits adultery, if he publicizes it, it is permissible to mention his sin and expose him for a benefit or deterrence. However, if he does not publicize it, it is obligatory to conceal his sin and advise him, and whoever slanders him without proof deserves the hadd punishment for slander. A Muslim should guard his tongue and not pry into people's private affairs or expose them.