a sister prays to Allah not to allow her husband marry a second wife. is it permissible?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Marrying more than one wife (polygyny) is a matter that Allaah has made permissible and there are much wisdom and great objectives behind it; we have mentioned some of them in Fatwa 86818.
Therefore, if the husband is able to be just between his wives and fulfill the requirements of polygamy, like spending on them and the like, then he may marry a second, third or fourth wife. So, a wife should not supplicate that her husband would not marry a second wife especially if the husband is in need of marrying a second wife in order to have children and the like. For more benefit, please refer to Fatwa 101485.
If this sister wants to use a supplication implying this, it is better for her to use a supplication like 'O Allaah make my husband satisfied with me only’, or ‘O, Allaah protect me from the harm of his second wife’ and the like.
Allaah Knows best.
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