Section 1: Permanent Prohibited Marriages

1- Due to blood relationship:

No man can marry a woman that he is forbidden to marry permanently because of blood linkage, namely:
(a) The mother, no matter how far the line of ascendant reaches, 
(b) The daughter, no matter how far the line of descent reaches, 
(c) The sister, be she was full sister, paternal half-sister or maternal half-sister, 
(d) The paternal aunt, be she was a full paternal aunt or paternal half-aunt, 
(e) The maternal aunt, be she was a full maternal aunt or paternal half-aunt, 
(f) The daughter of one’s brother, no matter how far the line of descent reaches, 
(g) And the daughter of one’s sister, no matter how far the line of descent reaches. This is a matter of agreement, and the consensus on this ruling was transmitted by al-Tabaree and Ibn al-Munthir.
- The daughter who is born outside the wedlock: 
The majority of scholars hold the view that it is forbidden for a man to marry his biological daughter that was a result of fornication or adultery. This is the view of the Hanafi, Maliki, and Hanbali and one of the views within the Shafi’i Madhab.

2. Due to marriage:
a. Mother-in-law:
i.
If the marriage is consummated with her daughter: It is prohibited for the man to marry his mother-in-law if he has consummated the marriage with her daughter. Al-Tabaree, Ibn al-Munthir, Ibn ‘Abd al-Barr and Ibn Hazm reported the consensus of scholars on this ruling.
ii. If the marriage is not consummated with her daughter: The four Madhabs agree that it is prohibited for the man to marry his mother-in-law upon conducting his marriage contract with her daughter.
b. Stepdaughters: [47] In Islam, stepdaughters are called Rabaaib; it is a plural of “Rabeebah” which means the girl who is being nurtured by her stepfather.
The four Madhabs agree that it is forbidden for the man to marry his stepdaughter if he has consummated the marriage with her mother, whether the stepdaughter was under his guardianship or not.
c. Son’s wife: The scholars are in agreement that the man is prohibited from marrying his son’s wife, even if the son has not consummated his marriage with her, so long as the marriage is conducted. The consensus has been transmitted by al-Tabaree, Ibn al-Munthir, Ibn Hazm, Ibn ‘Abd al-Barr and Ibn Taymiyyah.
d. Stepmother: The scholars are in agreement that the man is prohibited from marrying his stepmother, even if the father has not consummated the marriage so long as his father has conducted his marriage with her. The consensus has been transmitted by al-Tabaree, Ibn al-Munthir, Ibn Hazm, Ibn ‘Abd al-Barr and Ibn Taymiyyah.

3. Due to breastfeeding: The four Madhabs agree that the people who become forbidden to marry through breastfeeding are: his mother, his daughter, his sister, his nieces, his paternal aunts,  his maternal aunts, the mother of his wife, the daughter of his wife, the wife of his father, and the wife of his son.

4. Due to imprecation (li’aan): [48] In Islamic law, Li’aan takes place when a man accuses his wife of committing adultery or denies the paternity of a child borne by the wife, without providing legal proof. The procedure requires the man to declare four times under oath that he is truthful in his accusation and a fifth time, he would invoke Allah’s wrath upon himself, if he were to lie. In response, the woman shall be considered as guilty unless she declares under oath that the accusation is false, and a fifth time she would invoke Allah’s wrath upon herself if he was telling the truth. The outcome of this is that both will be separated, and the paternity will be denied. The majority of scholars hold the view that the woman becomes permanently forbidden for her husband upon the occurrence of imprecation, even if afterwards the husband confesses that he lied. This is the view of the Maliki, Shafi’i, and Hanbali Madhabs and the view of Zufar and Aboo Yusuf from the Hanafi Madhab.