I want to know if a woman can become forbidden to her husband. For example, if someone says he divorces his wife forever at once.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The scholars of Islam have different opinions regarding the husband who says to his wife: "You are forbidden to me (as a wife) forever."; or any expression that has the same meaning.

The Maaliki School of jurisprudence – in one of their opinions – believe that this is considered similar to divorcing her three consecutive divorces. So, the husband cannot return her to wedlock life unless she marries another man a serious marriage and he consummates the marriage with her, and then he divorces her or dies.

In their second opinion, the Maaliki School believes that this is an irrevocable divorce and her former husband can remarry her with a new contract, the consent of the Wali and a Mahr (bridal money) if he has not divorced her twice before. This last opinion is the one that the Maaliki School follows in their jurisprudence.

Some scholars believe that this matter depends on the intention of the husband. If he meant divorce, then this is a divorce; if he meant Dhihaar (saying to one's wife: you are forbidden to me as is the back of my mother is forbidden to me) then it is Dhihaar. But if he didn't intend any of the above, then it is considered like an oath and the husband expiates for that by an oath expiation.

But the most preponderant opinion of the scholars is that in a similar situation, the husband expiates for Dhihaar. Allah Says (what means): {And those who pronounce thihar from their wives and then [wish to] go back on what they said - then [there must be] the freeing of a slave before they touch one another. That is what you are admonished thereby; and Allah is Acquainted with what you do. And he who does not find [a slave] - then a fast for two months consecutively before they touch one another; and he who is unable - then the feeding of sixty poor persons. That is for you to believe [completely] in Allah and His Messenger; and those are the limits [set by] Allah. And for the disbelievers is a painful punishment.} [Quran 58: 3-4]

Allah knows best.