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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
A child from Zina (fornication) does not inherit from the man who committed Zina with the child's mother even if that man married her afterwards because he is not his son according to the Islamic law as we have already clarified in Fatwa 84788.
The right to inherit is based on affirmed marital relation and the child from Zina is not attributed to the fornicator according to the view of the majority of scholars, so he does not inherit from him. However, some jurists are of the view that if the woman who committed Zina is not married, the child from Zina is attributed to the fornicator and he inherits from him if the fornicator attributed the child to himself. Other jurists are of the view that the child inherits from him if the Hadd (the punishment determined by Islamic law for Zina) is implemented on the fornicator. At Islamweb, we adopt the view of the majority of scholars.
The Encyclopedia of Fiqh reads: "Jurists agreed that the child born out of wedlock is entitled to inherit from his mother and her relatives and they also inherit from him according to the share specified to them in the Islamic law or by Ta‘seeb (i.e. without having an allotted share, so they get what is left after the allotted shares have been distributed); and his paternal relatives are the paternal relatives of his mother.
As regards him inheriting from the fornicator and his relatives, the majority of the scholars are of the view that it is forbidden because he has no blood relationship with them, and that relationship is the legal cause for inheriting from each other. Therefore, if a man commits Zina with a woman and she gives birth to a child and then marries that same woman afterwards and she gives birth to a second child, then the two children would be half-brothers from the mother's side, and they inherit from each other only according to this basis. However, Al-Hasan and Ibn Seereen said that the child born from Zina is attributed to the fornicator if the Hadd is implemented on him, and he (the child) inherits from him in this case." [End of quote]
The Encyclopedia of Fiqh also reads: "Is-haaq ibn Raahawayh, Ibn Taymiyyah and others are of the view of that the relation of the child of Zina to the one who fornicated with the woman who is not married is affirmed because his fornicating is a confirmed reality; so in the same manner that the child's relation to the mother is affirmed, the relation to the fornicator is also affirmed so that the lineage of the child is not lost and he is not harmed and shamed for a crime which he did not commit as Allaah says (what means): {…and no bearer of burdens will bear the burden of another.} [Quran 6:164] This view necessitates that inheritance between the child and the fornicator is affirmed because inheritance is based on the affirmation of lineage, and they (these scholars) affirm it in the situation mentioned." [End of quote]
To sum up, according to the view of the majority of scholars, those children who were born from Zina have no right to inherit from your father, but if he makes a bequest to them that does not exceed a third of the estate, then it is effective because it is a bequest to a non-heir.
Allaah Knows best.