When is the parentage of the father proven?

Illegitimate children are those born as a result of sexual immorality. Here, the rights of parentage naturally belong to the mother and not to the father. Thus, the child should only inherit from its [mother’s] side because the child’s relationship with her is beyond doubt.

Regarding the relationship between an illegitimate child and his or her father, the majority of scholars deny its legal validity, even if the father confirms that the child is his. The reason for this is that [within the framework of a legally valid marriage], parentage is a ‘blessing’ whereas sex outside of marriage is a moral crime, which should not lead to [or be described as] a blessing. However, if the father confirms that a child belongs to him, and does not mention that he or she was born outside of marriage – and the conditions that confirm his declaration are present – then, on these grounds, the child will be treated as his [according to Islamic law]. This decision will rectify [the original sin], and if one of them dies, the other will inherit.

According Ishaq Ibn Rahwiya, Ibn Taymiyya and others, such a relationship is legally valid. They argue that, as sexual immorality is a concrete reality, we may assume that [if a man asserts his paternity of the child] it will become as apparent as that of the mother. In this sense, the family tree is not broken, and the child will suffer neither harm nor disgrace for a crime he or she did not commit. God the Almighty says: “Say: Shall I seek another than Allah for Lord, when He is Lord of all things? Each soul earneth only on its own account, nor doth any laden bear another's load. Then unto your Lord is your return and He will tell you that wherein ye differed” [6: 164].

According to this second opinion, the child inherits from his father and his father from him. Inheritance is a natural condition of [the workings of] the family tree. Hence, according to these scholars [Ishaq ibn Rahwiya and Ibn Taymiyya] the child is legally acknowledged and is therefore able to inherit from his father [despite the latter’s act of immorality].