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.