And this accords with what we have mentioned: wrongdoing has three levels—associating partners with Allah, wronging others, and wronging oneself. Killing is a wrong against others; when the victim is one’s own child, who is a part of oneself, it combines both kinds of wrongdoing. Adultery is a wrong against oneself, but when committed with one’s neighbour’s wife, it too combines both kinds. Nevertheless, the predominant wrong in killing is against another person, whereas in adultery it is against oneself.

For this reason, the right to retribution belongs to an individual, who may choose either to exact it or to pardon the offender. The prescribed punishment for adultery, by contrast, is a right of Allah in which no individual has a specific entitlement. Yet certain forms of adultery may be accompanied by, and lead to, circumstances harmful to others, making them graver than a killing that harms only the person killed.

Moreover, killing may admit of interpretive justifications that do not arise in adultery, for lawful sexual relations are clearly distinguished from unlawful ones. Killing, by contrast, includes cases that are clearly forbidden, others that are clearly obligatory, recommended, or permissible, and still others that are ambiguous. Thus Allah made a qualification concerning killing that He did not make concerning adultery, saying:

“Nor kill a soul…”—and the rest of the verse.
[Surah al-Furqān 68]