The origin for the women with whom marriage is prohibited, has to be, and is clearly mentioned, in the Kitab and Sunnah. As for the Kitab, Allah (swt) says: “And marry not women from whom your fathers married, except what has already passed; indeed it was shameful and most hateful, and an evil way .” [An- Nisa: 22] And He (swt) said:
“Forbidden to you (for marriage) are: your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters, your foster mother who gave you suck, your foster milk suckling sisters, your wives' mothers, your step-daughters under your guardianship, born of your wives to whom you have gone in - but there is no sin on you if you have not gone in them (to marry their daughters), the wives of your sons who (spring) from your own loins, and two sisters in wedlock at the same time, except for what has already passed; verily, Allah is Oft-Forgiving, Most Merciful. Also (forbidden are) women already married, except those (captives and slaves) whom your right hand possesses. Thus has Allah ordained for you. All others are lawful”. [An- Nisa: 23-24]
As for the Sunnah, Abu Hurayra has reported that the Messenger of Allah said: “One should not bring together a woman and her father’s sister, nor a woman and her mother’s sister in marriage”. Muslim narrates that 'Aisha (ra) said that the Messenger of Allah (pbuh) said: “Suckling makes women unlawful (for marriage) the same as birth makes unlawful.”
Thus, the marriage to mothers is absolutely forbidden. The mothers are everyone to whom you are related by childbirth. This is so, whether the one whom you are related to qualifies for the true word 'mother' which is the one who gave birth to you or she is a metaphorical mother i.e. is the one who gave birth to the one who gave birth to you and even if she is higher (in the line of descent)/and beyond. Therefore, your grandmothers: your mothers' mother and your fathers mother; the grandmothers of your mother and father; and the grandmothers of your grandmother and grandfather and even higher, irrespective of whether they are entitled to inheritance from you or not, they are all metaphorical mothers to whom marriage is prohibited.
Marriage to daughters is absolutely forbidden. They are every female who is related to you by your birth, such as the daughter who springs from your own loins or the daughters of sons and daughters, even if they go down in the line of descent. Whether they inherit or not, they are all daughters to whom marriage is forbidden.
Also absolutely forbidden to marry are the sisters from three directions; from the (same) mother and father or from (just) the father, or (just) the mother (uterine sisters).
Marriage to paternal aunts, the sisters of the father from three directions are forbidden, also the sisters of grandfathers through the father or mother, whether the grandfather is immediate or distant and whether He inherits or not.
Marriage to maternal aunts, the sisters of the mother from three directions are forbidden, also sisters of grandmothers and whosoever is higher in the line of descent, because every grandmother of a mother, and likewise every sister of a grandmother is considered a maternal aunt to whom marriage is prohibited.
Marriage to nieces and any woman who is related to the brother by birth is forbidden; so the daughter of a brother is forbidden from whatever direction the brother may be. The daughters of the sister are likewise forbidden.
Marriage to foster mothers is forbidden. They are the ones who have suckled you, their mothers and grandmothers, and whosoever is higher in the line of descent according to what has been mentioned in the genealogy. Every woman whose mother has suckled you or whom your mother suckled, or she and you have been suckled by the same woman, or you and she were suckled from the milk of the same man. Even if there were more than one foster mother. Such a woman is your sister and it is forbidden for you to marry her.
Marriage to the mothers of wives is forbidden. Whoever married a woman then everyone who is a mother to her by lineage or suckling, whether close or distant (in relation) becomes forbidden to Him by the existence of a mere contract irrespective of whether He has consummated the marriage or not. This is due to what has been narrated by 'Amr b. Shu'ayb, on the authority of his father who narrated on the authority of his grandfather that the Prophet (pbuh) said: “Whoever marries a woman and then divorces her before He has consummated the marriage with her, there is no objection to Him marrying his step-daughter (the woman’s daughter) but it will not be permitted for Him to marry her mother.”
Marriage to daughters of wives with whom He has consummated the marriage is forbidden. They are the stepdaughters. They are not forbidden except by consummation of the marriage with their mothers. They include every daughter of the wife by lineage, suckling, close or distant (in relation), whether inheriting or not, according to what has been mentioned concerning the daughters. If the marriage is consummated with the mother, then the daughters become forbidden for Him, whether they were under his guardianship or not, because the statement “Your step-daughters under your guardianship” [An- Nisa: 23], is a description of their general state and it is not mentioned as a condition. As for the statement: “born of your wives to whom you have gone in”. [An- Nisa: 23] This comes in the form of a condition, due to what is clearly mentioned after it: “... but there is no sin on you if you have not gone in them (to marry their daughters)”. [An- Nisa: 23] Therefore, if He has not consummated the marriage with the woman, then marriage to her daughter is not prohibited.
In addition marriage to daughters-in-law is absolutely forbidden, i.e. marriage to wives of his sons and wives of his grandsons through lineage, suckling, whether close or distant (in relation), the moment the contract was concluded, irrespective of whether the marriage was consummated or not.
Marriage to one's step-mothers is forbidden. Therefore, a man is forbidden from marrying the wife of his father whether He is a close or distant relation, whether He is entitled to inheritance or not and whether He is related by lineage or suckling. An-Nisai has reported that al-Barra' b. 'Azib said: “I came across my maternal uncle who was carrying a (war) banner. I said: ‘what do you wish to do?’ He said: ‘The Messenger of Allah ordered me to go to a man who had married his father’s wife after his death, in order to strike his neck (i.e. kill Him).’’’
It is prohibited to be married to two sisters at the same time, whether they were sisters because of lineage, suckling, from the same mother and father, from one father or one mother, and irrespective of whether the marriage to the sister took place before or after consummation. If He marries them both in a single contract then the contract will be improper (Fasid).
It is also forbidden to be married to a woman and her paternal or maternal aunt at the same time. This is because of what has been narrated by Abu Hurayra that the Messenger of Allah said: “One cannot be married to a woman and her paternal aunt, or a woman and her maternal aunt at the same time”. And in the narration of Abu Dawood: ‘A woman and her paternal aunt, a paternal aunt and her brother’s daughter, or a woman and her maternal aunt and a maternal aunt and her sister’s daughter cannot be married to the same man at the same time. Neither the older after the younger, nor the younger after the older can be combined in marriage.”
In addition it is also forbidden to marry women that are already married. Allah has called them 'Al-Muhsanat' (chaste women) because they have protected their private parts (from Zina) through marriage.
Suckling prohibits that which lineage prohibits. Every woman that is forbidden due to lineage, likewise is also forbidden due to suckling. This applies to mothers, daughters, sisters, paternal and maternal aunts, and nieces (daughters of the brother and sister). They are forbidden in the same manner as in the prohibition of lineage due to the saying of the Prophet (pbuh): “What is forbidden by lineage is likewise forbidden by suckling”. And in the narration of Muslim: ‘Suckling makes unlawful what birth makes unlawful’(in terms of marriage). And 'Aisha (ra) narrated that: “Aflah, the brother of Abu al-Qu’ays, asked me permission (to enter the house) after the partition (Hijab) was revealed. So I said: ‘By Allah, I would not admit Aflah unless I have asked the opinion of Allah’s Messenger (pbuh) on this matter, for the brother of Abu al-Qu’ays has not suckled me but it was the wife of Abu al-Qu’ays who suckled me’, when Allah’s Messenger (pbuh) came, I said: ‘O Messenger of Allah! It was not the man who suckled me but it was his wife’ He said: ‘Permit Him to enter for He is to you a (paternal) uncle, you may have perished, had you not asked.’” The prohibiting factor in suckling is the milk. So both the owner of the suckled milk and the one who made suckling are prohibited to the person who was suckled. Whether the owner of the milk was a man or a woman, and whether the one who was suckled was child for whom He suckled from or not. Consequently, it is allowed for a person to marry his foster brother's sister but not allowed to marry his/her foster brother or sister. So, if a person was breast fed from a woman, this woman will be his foster mother and her husband will be his/her foster father. Their children (both sons and daughters) will be his foster brothers and sisters, while the brothers of the person who was suckled are not brothers and sisters of his/her foster brothers and sisters. Therefore, they are allowed to marry the foster brothers and sisters of their brother. Thus the prohibiting factor is the milk.
These are the women to whom marriage is forbidden, and any women other than these are permitted for marriage. This is due to his (swt)'s saying:
“All others are lawful (for marriage)” [An- Nisa: 24]
This as explained earlier, excludes the marrying of a Mushrik and a woman who is already married.