What is the religious ruling on killing one's sister or daughter if she commits adultery?

Adultery is a grave sin, and its perpetrator is wicked. The execution of the prescribed punishment for it is the prerogative of the Sharia (definition) judiciary. Whoever kills his unmarried (non-muhsana) sister who committed adultery is sinful and has committed a great transgression. He will be subject to retribution (qisas) unless the guardians of the victim's blood (awliya ad-dam) pardon him, and he must repent and seek forgiveness. However, if she was married (muhsana), the judiciary must be presented with evidence (a valid confession or four upright witnesses who clearly saw her committing the indecency). If this is proven, then he is not liable for blood money (diyah), qisas, or expiation (kaffara); however, he is sinful for usurping the authority of the ruler and shall be disciplined (ta'zeer) for that. A father who kills his adulterous daughter is not subject to qisas, but the ruler may discipline him. The matter of killing is grave; Allah Almighty says: (And whoever kills a believer intentionally - his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment).