"You are haram to me." It is zihar if he intended zihar by it, and comparison to someone forbidden is a prohibition, thus it is zihar. As for the menstruating woman, enjoyment is permitted with her in areas other than the vagina, and for the woman in ihram, it is permissible for him to look at her and touch her without desire, and there is no hadd (prescribed punishment) for having intercourse with either of them, unlike our issue. Abu Bakr chose the view that zihar only occurs from those who are mahrams (permanently forbidden women) [among women, not from men]. He said: This is what I hold.

Section: If he compares her to the back of his father, or [to the back of someone else] among men, or says: "You are to me like the back of a beast," or "You are to me like carrion and blood," there are two narrations in all of these; one of them is that it is zihar. Al-Maymuni said: I said to Ahmad: "What if he performs zihar using a man's back?" He said: "A man's back is haram, so it is zihar." Ibn al-Qasim, the companion of Malik, said the same in the case where he says: "You are to me like my father's back." This is also narrated from Jabir ibn Zayd. The second narration is that it is not zihar, which is the opinion of the majority of scholars, because it is a comparison to something that is not a place for enjoyment, so it resembles if he had said: "You are to me like Zayd's wealth." Is there an expiation for it? There are two narrations; one of them is that there is an expiation because it is a type of prohibition, so it resembles if he had forbidden his wealth. The second is that there is nothing upon him. Ibn al-Qasim transmitted from Ahmad, regarding one who compares his wife to a man's back: It is not zihar, and I have not seen him obligate anything for it; this is because it is a comparison of his wife to something that is not a place for enjoyment, resembling a comparison to someone else's wealth. Abu al-Khattab said [regarding his saying]: "You are to me like carrion and blood": If he intended divorce by it, it is a divorce; if he intended zihar, it is zihar; if he intended an oath, it is an oath; and if he intended nothing, there are two narrations: one of them is that it is zihar, and the other is that it is an oath. The meaning of intending zihar and an oath did not become clear to me. And Allah knows best.