Here is a table of forbidden marriage with close relatives, and the table agrees mainly with what is usually accepted among all nations. The prohibition is due to: 1- blood relationship or consanguinity. 2- Fostrage or milk relations. 3- The relatives in - law.
Those related by blood, or the consanguineous are of seven groups: mother, daughter, sister, paternal aunt, maternal aunt, your brother's daughter, and your sister's daughter. Mother includes grand mother through the father or mother, great - grandmother and etc.
Daughters too, includes grand daughter through son or daughter, great- grand- daughter and so on.
Then the fostrage and milk - relatives are named in the table; `Your foster- mother who have given suck to you, and also your foster- sister.'
In the third stage there comes in the verse the relatives- in- law, who are mentioned in four groups:
1- `your wife's mothers.' This implies that as soon as you marry a girl, her mother and grand-mother, and going on, her great grand- mother will be unlawful for you in marriage for ever.
2- Your step- daughter under your guardianship, and born of your wives with whom you have made love - but if you have not made love with her there is no guilt on you if you marry her daughters.
3- And taking in marriage two sisters in the same time and simultaneously. Here an exception is pointed to: ``and that is what had already been done and passed. This was because during the Pagan Era, it was very customary for an Arab to marry with two sister simultaneously and at the same time.''