inuit … this webpage (Islam Web) quotes the books that talks about what I said ..
**Islam forbids marriage between the brothers and the sisters. Allah Says (interpretation of meaning): Forbidden to you (for marriage) are: your mothers, your daughters, your sisters .. [4:23].
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The above ruling is in our Shariah and every Prophet has his own Shariah. Hence, it was lawful in the Shariah of Adam that a man married a woman who was not his twin. It is reported in the Books of Tafseer like al-Tabri, al-Qurtubi, Ibn Katheer, al-Bidaya Wa al-Nihayah that every time Hawa (Eve) used to give birth of twins; a boy and a girl. Adam was ordered to marry his male child to his female one who was not the male’s twin.