What is the ruling regarding a man saying: "It is unlawful for me from my wife's back" if he prepares this dinner and she partakes of it, even though he has not yet consummated the marriage after the عقد (marriage contract)?

The husband's statement: "My wife's back is unlawful to me" is a prohibition of his wife, and prohibition does not admit of partiality. If he intended divorce, then it is effective, and his wife becomes irrevocably divorced from him. If he intended zihar, then he must offer expiation before having intercourse with her. If he intended an oath or did not intend anything, then he is bound by an expiation for breaking an oath.