The eminent Muslim scholar and renowned Da`iyah, Sheikh `Abdel Khaliq Hasan Ash-Shareef, states: “If this happens, a Muslm husband should know that there is no effect of what the father did on the validity of his marriage nor the attribution of his children to him. The saying that the marriage is already invalid and the child and future generations are haram is baseless and has no ground or evidence in Shari`ah. Even if actual zina had taken place, this does not render the wife haram for the husband.
Therefore, it should be clear that there is no effect of what happened on marriage and the childen are fruits of the marriage and no one has the right to oblige the husband to divorce his wife. It would be far better for the sinful father to stay away from his son and his wife and to focus on coming back to Allah and asking Him for repentance.
Under these circumstances, husbands have the right to prevent the father from visiting his home and to meet him in another place. But, he also has to keep relations and good contacts with him and to ask Allah Almighty to guide him and us all to the right path.”