What happens if a man conditions the divorce of his two co-wives upon divorcing one specific wife?
Chapter on Explicit Divorce and Others
Al-Mughni
Book of Divorce
Primary text
If a man states to Zainab: If I divorce you, your two co-wives are divorced. Then he says the like to Umrah, and the like to Hafsah. If he then divorces Zainab, each woman is divorced once. This is because he did not initiate divorce upon anyone other than Zainab; the co-wives were divorced based on a prior condition established upon Zainab's divorce.
Supporting text
If he divorces Umrah, Zainab is divorced once, and Umrah and Hafsah are each divorced twice. Umrah is divorced once directly, and once each because of Zainab's and Hafsah's divorces. Zainab and Hafsah are each divorced once because Umrah's divorce is an initiating divorce upon them, resulting from a condition he established after conditioning their divorce upon hers. This results in two divorces for Umrah and Hafsah, but does not result in a second divorce for Zainab because their divorces resulting from the condition are not considered initiating divorces upon her.