What is the ruling on someone who says to his wife: "If you go to my mother, you will be divorced," and what is the expiation for that?

The ruling on suspending divorce upon the wife's visit to her mother varies according to the husband's intention. If he intended the divorce to take effect upon her departure, then the majority of scholars hold that the divorce occurs when the condition is met, and this is the preferred view. However, if he did not intend the divorce to take effect, but rather intended deterrence or prevention, then Shaykh al-Islam Ibn Taymiyyah is of the opinion that the divorce does not occur, and an expiation for a broken oath (kaffarat yamin) is due. If his intention was merely a promise to effect a divorce if she committed the forbidden act, then nothing results from that, because a promise of divorce is not a divorce.