Does divorce take effect and the third repudiation count if the husband said to his son: "If you speak to so-and-so, then your mother is forbidden to me as if she were my sister, and she is divorced," and the son spoke to so-and-so, knowing that she has already been repudiated twice?

If a husband made the validity of his pronouncement of ẓihār upon his wife and her divorce contingent on his son speaking to someone, and the son did speak to that person, then the ẓihār and divorce take effect. If this divorce is the third, following two previous divorces, the wife becomes irrevocably separated (baynūnah kubrā) and is not permissible for her first husband until she marries another man out of genuine desire, and he consummates the marriage with her, and then he divorces her or dies, and her ʿiddah (waiting period) expires. If the first husband wishes to remarry her after that, he must perform the expiation for ẓihār.

However, if the husband did not intend to effect a divorce but rather intended to threaten or prevent, some scholars, like Ibn Taymiyyah, hold that the divorce does not take effect, and the husband is only required to perform the expiation for breaking an oath (kaffārat yamīn).

Furthermore, there is a difference of opinion among scholars regarding the occurrence of the breach of oath if the son spoke to the intended person while forgetting his father's oath.