Does incest nullify marriage? e.g.: A man had sex with his daughter does this nullify marriage with his wife.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The scholars differed in opinion concerning the one who committed Zina (fornication or adultery) with his mother-in-law or with the daughter of his wife, whether or not his wife becomes forbidden for him.

'Ikrimah said concerning a person who had sex with his mother-in-law that he commits double sin but his wife does not become forbidden for him. Ibn Hajar said: "Its chain of narrators is Saheeh [authentic]."

There is also a Hadeeth which reads that the Prophet was asked about a person who had indulged in illegal sex with a woman, can he marry her mother, or that he commits illegal sexual intercourse with the mother, can he marry her daughter? The Prophet   answered: "What is forbidden does not make what is lawful forbidden." [At-Tabaraani and Ad-Daaraqutni] However, the chain of narrators of this Hadeeth is weak.

Nonetheless, Ibn Maajah reported part of this Hadeeth with an authentic chain of narrators.

Besides, it was reported that Ibn 'Abbaas was asked by a man who committed Zina with his mother-in-law, and he [Ibn 'Abbaas] told him: "Your wife becomes forbidden for you." The same thing was reported by Abdur-Razaaq from Al-Hassan Al-Basri .

Moreover, Qataadah said: "His wife does not become forbidden for him but he should not have sexual intercourse with his wife until the waiting period of the woman with whom he had committed Zina expires."

Nonetheless, Abu Haneefah and his followers, 'Ataa', Al-Awzaa'i, Ahmad, Ishaaq and Malik in a narration, are of the view that a man who committed Zina with his mother in law, his wife becomes forbidden for him.

For more benefit, please refer to Fatwa 91451.

However, the majority of the scholars did not agree with this opinion. Their evidence is that marriage in the Sharee'ah refers to a man who has conducted a marriage contract with a woman and does not refer to having sexual intercourse with her.

Also, there is no dowry, no waiting period and no inheritance in Zina.

Ibn Abdul Barr said: "The scholars specialized in issuing Fataawa agreed in a consensus that it is not forbidden for a man who committed Zina with a woman, to marry her [same woman]. Thus, it is more lawful to get married with her mother or daughter."

On the other hand, Imaam Ash-Shaafi'i said: "If a man had illegal sex with a woman, she does not become forbidden for him if he wants to marry her, he may even marry her mother or her daughter. This is because Allaah forbade marrying the mother and daughter of the woman whom he marries not the one with whom he committed Zina."

Allaah knows best.