The husband becomes mahram to the girl breastfed by his wife if she feeds her five times or more and the child is less than two years.

However, regarding adoptions in Islam:

Adoption is not permissible in Islam. It is permissible and recommended to support an orphan and to raise him up but not as a son but as an orphan who doesn’t relate to those who took him in.

If a couple adopt a girl, and the wife breast-feeds the girl, would the husband then become mahram to the girl?

Mahram | June 20, 2017 5:31 am
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in islam who is financially responsible for the maintanance of an unmarried female whos closest male relatives are her brothers (heirs). Males receive a 2:1 share of their parents inheritance. As they are protectors and maintainers of women. Does this verse cover all females or only apply to wives and secondly does it exclude females who work? Be that a daughter or sister?
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I was wondering if my 13 year old step brother is my mahram until he turns 14/15? because currently I do not wear a scarf in front of him because i read it is only when he reaches puberty or the age of 15 that he becomes non mahram. is this true or even do i still have to observe hijab even though he is 13?