What should the person whose mother or father was insulted do regarding the one who insulted them?

Reviling a Muslim is an act of transgression (fisq), and fighting him is disbelief (kufr). It deprives the reviler of his good deeds and enables the wronged to exact justice from him on the Day of Resurrection. The wronged party is permitted to respond to reviling in kind, as long as it does not involve disbelief or falsehood. However, he is not allowed to revile the parents of the reviler, as this constitutes injustice towards innocent individuals. The preferred course of action is to pardon, overlook, and supplicate for the wrongdoer, following the example set by the Quran and the Prophetic Sunnah (definition). "And whoever pardons - his reward is due from Allah."