the Holy Qur'an

Also (prohibited are) women already married, except those whom your right hands possess: Thus hath God ordained (Prohibitions) against you: Except for these, all others are lawful, provided ye seek (them in marriage) with gifts from your property,- desiring chastity, not lust, seeing that ye derive benefit from them, give them their dowers (at least) as prescribed; but if, after a dower is prescribed, agree Mutually (to vary it), there is no blame on you, and God is All-knowing, All-wise. (4:24)

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