with whom marriage is Ḥarām forever, no matter whether she is not allowed to marry them due to a blood relation or due to another reason such as breast-feeding (Raḍā’at) or Muṣāĥarat.
Question: Who exactly are Maḥārim?
Answer: Maḥārim include three types:
1. Those with whom Nikah is Ḥarām forever due to a blood relationship.
Those with whom Nikah is Ḥarām due to the relation formed on the basis of Raḍā’at.
Muṣāĥarat: Those with whom Nikah is Ḥarām due to a marital relationship, such as a daughter-in-law for her father-in-law or a son-in-law for his mother-in-law.
Another way to understand Muṣāĥarat is that when a woman marries a man, it is Ḥarām forever for her to marry his fathers (father, grandfather, great grandfather etc.) and sons (son, grandson, great grandson etc.). Similarly, a husband can never marry the mothers or daughters of his wife. Also the same rules of Muṣāĥarat apply if a man or woman commits fornication or indulges in any act leading to fornication (e.g. lustfully touching or kissing someone’s naked skin).
Excluding Maḥārim blood relatives, observing veil in front of the other two Maḥārim is neither prohibited nor Wājib. However, if a woman is young or there is a possibility of indecency, then she should observe veil with these two.