The practice of comparing the back of one's wife to that of one's mother as a method of divorce was known as
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The practice of comparing the back of one's wife to that of one's mother as a method of divorce is known as "Zihar" in Islamic law. Zihar is a form of divorce in which a husband compares his wife to his mother in order to declare that he will no longer have any sexual relations with her. This was considered a derogatory and insulting statement in Arab culture, and was thus recognized as a valid ground for divorce.
Under Zihar, the husband had to make a formal statement to this effect, after which the couple would be considered separated, and the woman could go back to her family. This practice has been abolished in many countries, including most Muslim-majority countries, as it is considered a form of verbal abuse and goes against the principles of gender equality.