What is the ruling on a conditional divorce pronounced with the formula, "If you do such and such, you are divorced," and what is its evidence, and is expiation (kaffarah) required for it?

If a man says to his wife: "If you do such and such, you are divorced," then if the wife does not do the thing conditioned, divorce does not occur. However, if she does it, divorce occurs according to the majority of scholars. Some scholars, such as Ibn Taymiyyah, are of the view that if the husband did not intend divorce but rather intended prevention or threat, then he must offer expiation for breaking an oath.