What is the ruling when a husband compares his wife to the back of a woman forbidden to him permanently due to reasons other than direct kinship (e.g., foster mother or father's wife)?

Primary text

Comparing the wife to the back of a woman forbidden permanently due to reasons other than blood relation—such as a foster mother, a foster sister, a father's wife, a son's wife, or a stepdaughter whose mother the husband has consummated—also constitutes *Zihar*. The dispute regarding this category mirrors the dispute in the previous category concerning kinship relations. The view supporting this being *Zihar* is founded on the argument that foster mothers fall under the general term 'mothers' mentioned in the primary text, and the others share a similar legal meaning, thereby invoking the same ruling.