The father’s (ex-)wife is a mahram to his sons even if she did not bear him any children

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Check below answers in case you are looking for other related questions:
He is not sure whether he breastfed from her grandmother – may he marry her?
It is not permissible to marry a zaani or zaaniyah unless they have repented

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Related Answers:
Most of his maternal cousins were breastfed by his mother and he was breastfed by his maternal aunt; what is the ruling on his brother?
Is it permissible to marry two sisters from one father at the same time?
The sister of the wife’s grandfather and the sister of her grandmother are mahrams to the husband just as her paternal aunt and maternal aunt are mahrams to him
He is not sure whether he breastfed from her grandmother – may he marry her?
It is not permissible to marry a zaani or zaaniyah unless they have repented

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