PPC Section 79

Section 79. Act done by a person justified, or by mistake of fact believing himself justified, by law

Nothing is an offence which is done by any person who is justified by law, or who, by reason of a mistake of fact and not by reason of a mistake of law, in good faith believes himself to be justified by law in doing it.

Illustration:

A sees Z commit what appears to A to be a murder. A, in the exercise, to the best of his judgment, and in good faith, uses the power given by law to all persons to apprehend murderers in the act. A seizes Z in order to bring Z before the proper authorities. A has committed no offence, even though it may later turn out that Z was acting in self-defense.