Grounds on which marriage is prohibited:

1. Prohibition on the ground of Consanguinity
   • his mother or his grandmother how high so ever.
   • his daughter or his granddaughter how lo so ever.
   • his sister whether full, consanguine, or uterine.
   • his niece or grand-niece how low so ever.
   • his aunt or grand aunt how high so ever, whether paternal or maternal.
      
2. Prohibition on the ground of affinity:

   A man is prohibited from marrying:

   • his wife's mother or grandmother how high so ever.
   • his wife's daughter or granddaughter how low so ever.
   • the wife of his father or paternal grandfather how high soever.
   • the wife of his son or son's son or daughter's son how low soever.

   A marriage with a woman prohibited by reason of affinity is by a Muslim not void but irregular. A marriage with his wife's sister during the lifetime of the first wife is also irregular.
    

3. Prohibition on the ground of fosterage:

   It is unlawful for a Muslim (except in some cases) to marry a woman connected with him through an act of suckling, under 2 years of age, in such a way that if it had been an act of procreation, marriage with her would have been unlawful by reason of consanguinity or affinity. Whoever is prohibited by consanguinity or affinity is also prohibited by reason of fosterage, except for certain foster relations like foster mother, foster sister, etc. A marriage prohibited by fosterage is void.
    

4. Prohibition on the ground of difference of religion:
   • A Muslim male may contract a valid marriage with a Muslim woman or with a Kitabia, i.e., a Jewess or a Christian, but not with an idolatress or a fire-worshipper. However, if he marries an idolatress or a fire worshipper, the marriage is irregular, not void.
   • A Muslim woman cannot contract a valid marriage except with a Muslim. A marriage with a non-Muslim, whether a Kitabi or non-Kitabi, is irregular, not void.
      
5. Prohibition on the ground of unlawful conjunction:

   A man may not have at the same time two wives who are so related to each other that if either of them had been a male, marriage between them would have been prohibited by consanguinity, affinity, or fosterage. Unlawful conjunction renders a marriage irregular, not void.
    

6. Prohibition against marriage during Iddat:

   A marriage with a woman before the completion of her Iddat is irregular. At one time, such a marriage was regarded as void, but the later view is that it is only irregular, and the children are legitimate.