Koran 33:30:
O ye wives of the Prophet! Whosoever of you committeth manifest lewdness, the punishment for her will be doubled, and that is easy for Allah.
O Consorts of the Prophet! If any of you were guilty of evident unseemly conduct, the Punishment would be doubled to her, and that is easy for God.
O wives of the prophet! whoever of you commits an open indecency, the punishment shall be increased to her doubly; and this IS easy to Allah.
O wives of the Prophet! if any of you be guilty of manifestly dishonourable conduct, the punishment will be doubled for her. And that is easy for ALLAH.
Wives of the Prophet, whosoever among you commits a flagrant indecency, for her the chastisement shall be doubled; that is easy for God.
O wives of the Prophet! should any of you be guilty of a proven lewdness, doubly shall her chastisement be doubled: and with God this is easy.
O wives of the prophet, whosoever of you shall commit a manifest wickedness, the punishment [thereof] shall be doubled unto her twofold; and this is easy with God:
What would their punishment be to begin with?
There are only a handful of punishments prescribed in the Koran, but only one punishment for lewdness.
And that punishment - permanent home confinement - cannot be halved.