for a life’ (5:45). Thus, if someone kills another with rightful cause—that is, in retaliation for a life already taken—he incurs no blame and no sin. In such a case the killer may inherit from the slain, whereas a killer who shed blood unlawfully is barred from any inheritance.
Consider an example involving three brothers. The eldest deliberately murders the youngest. The estate of the youngest passes to the middle brother, while the eldest takes nothing, because he killed without right. The middle brother then pursues lawful retribution for the blood of his younger brother and kills the eldest in retaliation. Does the middle brother inherit from the eldest, even though he is the one who killed him? Yes, he does, because his act was lawful. By contrast, the eldest who killed the youngest inherits nothing, for his killing was unlawful.
A lawful killing therefore brings no reproach and leaves no legal taint, for it is qiṣāṣ (retaliatory punishment). Allah, exalted is He, says: ‘In qiṣāṣ there is life for you, O people of insight, so that you may become mindful’ (2:179).
As for His words, ‘or for spreading corruption,’ corruption in the land does not mean that someone simply hires an excavator to demolish a house, even if that demolition is wrongful. Although such an act is certainly corrupt, it does not make a Muslim’s blood lawful. True corruption on earth consists in disseminating evil ideas, promoting depraved doctrines, committing highway robbery, trafficking in narcotics, and the like. Whoever causes corruption of this sort has forfeited his life and is lawfully to be killed, for he is an active corrupter on earth. Indeed, in the same surah Allah the Most High says: ‘The penalty for those who wage war against Allah and His Messenger and strive to spread corruption in the land is that they be killed, crucified, or have their hands and feet cut off on opposite sides…’ (5:33), each punishment matching the gravity of the crime: if it is most severe, execution; if lesser, crucifixion; and if lesser still, amputation.