Swearing by divorce or making unlawful (one’s wife) is an oath of the Faasiqs
16-1-2014 | IslamWeb
Question:
In a state of anger I said to one of my children: "(I swear) By (making your mother) unlawful (for me), if you do so and so I will not let you go to such and such a place in the future." If he goes to such a place, will it be counted as one incident of divorce?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is not appropriate for a Muslim to swear by (making his wife) unlawful or by divorce or anything by which swearing is impermissible. If he wants to swear, he should swear by Allaah The Almighty, otherwise he should remain silent. It is narrated on the authority of ‘Abdullaah ibn Mas‘ood 
that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said: “If anyone has to swear, let him swear by Allaah, otherwise, let him remain silent.” [Al-Bukhari and Muslim]
Excessive swearing is criticized by the Quran as Allaah The Almighty Says (what means): {And do not obey every worthless habitual swearer.} [Quran 68:10]
Swearing by divorce or by making one’s wife unlawful is among the oaths of the Faasiqs (defiantly disobedient people). Some scholars say that if one swears frequently by divorce or by making his wife unlawful, his testimony should be rejected and he is to be judged as a Faasiq.
So, we advise the questioner to avoid swearing by divorce or by making unlawful his wife. If he is forced to swear, let him swear by Allaah or remain silent.
There is a difference of opinion among the scholars over the ruling on swearing by making one’s wife unlawful. Some opt for the opinion that a Thihaar expiation is due on him if he breaks his oath. Thihaar expiation is mentioned in the Saying of Allaah The Almighty (which means): {And those who pronounce Thihaar 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 Allaah 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.} [Quran 58:3-4]
Others are of the opinion that it is considered an irrevocable divorce.
It seems that the preponderant opinion, Allaah Willing, is the former in which the swearer takes the same ruling of the Thihaar pronouncer owing to the similarity between them.
Allaah Knows best.