Surah 24. An-Nur, Ayah 6

Lit., "then the testimony of any of these shall be four testimonies [or "solemn affirmations"] before God".

 In order to be spared the punishment for false accusation.

The case of married persons is different from that of outsiders. If one of them accuses the other of unchastity, the accusation partly reflects on the accuser as well. Moreover, the link which unites married people, even where differences supervene, is sure to act as a steadying influence against the concoction of false charges of unchastity particularly where divorce is allowed (as in Islam) for reasons other than unchastity. Suppose a husband catches a wife in adultery. In the nature of things four witnesses-or even one outside witness-would be impossible. Yet after such an experience it is against human nature that he can live a normal married life. The matter is then left to the honour of the two spouses. If the husband can solemnly swear four times to the fact, and in addition invoke a curse on himself if he lies, that is prima facie evidence of the wife's guilt. But if the wife swears similarly four times and similarly invokes a curse on herself, she is in law acquitted of the guilt. If she does not take this step, the charge is held proved and the punishment follows. In either case the marriage is dissolved, as it is against human nature that the parties can live together happily after such an incident.