Parentage of the child from another marriage or adultery

The fatwa of Jamiat al-Rashid appears to be consistent with the basic principle stated in Hakeemul Ummat Maulana Ashraf Ali Thanvi (RA)'s Beheshti Jeor. It is not Shariah to remarry while still having a valid nikah with the first husband; Such marriages are considered null and void and the relationship is included in jina. However, no one is called an infidel for this reason, until he denies the provisions of the Shari'ah.

A fundamental principle of Shari'ah in determining nasab (paternity of a child) is “الولد لفراش” meaning that the child will be attached to the side of the legitimate conjugal relationship. So if a child is born while the wife is still married to you, and after six months of marriage have passed, the child will be considered your child according to Shari'ah—even if there was no actual intercourse or adultery with someone else.

The important point here is that even if zina is proved in the court, the nasab of the child is not automatically annulled. The only Shariah method of severing nasab is “liyan” (لعان). So if you don't do Lian, the child will be linked to you and you will be considered as the father according to Shariat.

If you want to adopt the child, it is perfectly legal. Rather, the child will be considered as one's own child if the lien is not taken. Lien is not mandatory; This is done only when the husband wants to deny paternity. There is no problem in the eyes of Sharia if you accept. Note, however, that in real life such matters are also much more complex—legal, social, and evidentiary aspects are involved. If there is such a matter, a local reliable Darul Ifta should be directly contacted with the detailed situation and final guidance should be taken. If not, hopefully our answer is sufficient.