AFFINITY. Arabic Qurabah قرابة.
The prohibited degrees hurmah with regards to marriages are as follows: – Mother, daughter, paternal aunt, maternal aunt, brother’s or sister’s daughter, grandmother, granddaughter, mother-in-law, step mother, daughter-in-law, granddaughter-in-law. Nor can any man marry any who stand in any of these relationships from fosterage. The marriage of two sisters at the same time is forbidden, but the marriage of a deceased wife’s sister is allowed. Marriage with a deceased brother’s wife is very common in Muslim countries, such marriages being held to be a very honourable means of providing for a brother’s widow. The marriage of cousins is also considered most desirable, as being the means of keeping families and tribes together. The passage of the Qur’an on the subject of affinity, is as follows (Surah v.27)
“Marry not women whom your fathers have married: for this is a shame, and hateful, and an evil way :-though what is past (i.e. in times of ignorance) may be allowed.
“Forbidden to you are your mothers, and your daughters, and your sisters, and your aunts, both on the father and mother’s side, and your nieces on the brother and sister’s side, and your foster-mothers, and your foster-sisters, and the mothers of your wives, and your step-daughters who are your wards, born of your wives to whom ye have gone in: (but if ye have not gone in unto them, it shall be no sin in you to marry them;) and the wives of your sons who proceed out of your loins; and ye may not have two sisters; except where it is already done. Verily, God is Indulgent, Merciful!
“Forbidden to you also are married women, except those who are in your hands as slaves: This is the law of God for you. And it is allowed you, beside this, to seek out wives by means of your wealth, with immodest conduct, and without fornication. And we give those with whom ye have cohabited their dowry. This is the law. But it shall be no crime in you to make agreements over and above the law. Verily, God is Knowing, Wise!”
Based on Hughes, Dictionary of Islam