[4:20]

And if ye wish to exchange one wife for another and ye have given unto one of them a sum of money (however great), take nothing from it. Would ye take it by the way of calumny and open wrong ?

[4:21]

How can ye take it (back) after one of you hath gone in unto the other, and they have taken a strong pledge from you ?

[4:22]

And marry not those women whom your fathers married, except what hath already happened (of that nature) in the past. Lo! it was ever lewdness and abomination, and an evil way.

[4:23]

Forbidden unto you are your mothers, and your daughters, and your sisters, and your father’s sisters, and your mother’s sisters, and your brother’s daughters and your sister’s daughters, and your foster-mothers, and your foster-sisters, and your mothers-in-law, and your step-daughters who are under your protection (born) of your women unto whom ye have gone in - but if ye have not gone in unto them, then it is no sin for you (to marry their daughters) - and the wives of your sons who (spring) from your own loins. And (it is forbidden unto you) that ye should have two sisters together, except what hath already happened (of that nature) in the past. Lo! Allah is ever Forgiving, Merciful.