Is the son sinful for not searching for his father who disowned him?

A husband is not permitted to accuse his wife of adultery without evidence, especially incest, which is the most severe type of adultery. The default assumption for a Muslim is innocence, and harboring ill thoughts about them is forbidden. Legally, the child is the husband's child and can only be disclaimed through li'an (oath of condemnation). The husband must be advised to fear Allah and repent for what he has done. The wife should raise her son by clarifying that this man is his legitimate father, and that among the rights of a father over his child is to treat him kindly and pray for his guidance.