the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
It is a sin for a man to say that his wife that she is unlawful to him like the back of his mother. The Qur’ân describes this statement as “iniquitous and false.”
If a man says such a thing to his wife, he may not have sexual relations with his her again until after he frees a slave. If he is unable to do this (which is the case today in the absence of slaves), then he must fast two consecutive months before he can have sexual relations with his wife again.
He must fast. If he is truly and absolutely incapable of fasting, then and only then may he turn to the next form of expiation, which is the feeding of 60 poor people.
[Refer to: Sûrah al-Mujâdilah: 3-5]
Source: Islam Today