What is the ruling when a man issues the oath of Zihar (likening his wife to his mother) separately to each of his multiple wives?

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If a man issues the oath of Zihar using distinct pronouncements to each of his wives individually (stating to each, 'You are to me as my mother's back'), then each pronouncement necessitates a separate expiation (Kaffarah). This position is held according to the apparent meaning of the statement of Al-Khiraqi, and is the view adopted by Urwah and 'Ata. The rationale is that these are repeated oaths concerning distinct individuals, thus each requires its own expiation. This is analogous to one who offers expiation and subsequently repeats the Zihar. Furthermore, since the oath taken regarding one wife does not invalidate the oath taken regarding another, they cannot be covered by a single expiation, similar to the original oath. Additionally, Zihar is an act that mandates expiation, and expiation multiplies with the multiplication of the act in different instances, comparable to homicide, distinguishing it from a Hadd punishment which is averted by doubt.