What is the ruling regarding a wife saying to her husband: "If you do such and such, I am forbidden to you until the Day of Judgment, like the حرمة (inviolability) of my father and my brother"?

The answer to this question was previously provided in earlier fatwas. Attaching a condition to a prohibition does not change its unlawful nature, because what is forbidden in all circumstances remains forbidden even if conditioned on one circumstance over another. A conditional statement does not take effect unless its condition is met. Therefore, the expiation for an oath (kaffarat al-yamin) is not incumbent upon the wife merely for what she said; rather, it becomes incumbent upon her if the husband performs the action referred to.