Marriage between the Children of a Couple who had Committed Adultery

Question: A married man and married woman struck up an affair and even committed adultery with each other. They, however, repented and separated. A long time has now passed and the woman wishes to get her son married to the man's daughter. Is this permissible when it is certain that the son is not his?

Answer: His daughter from his wife may marry the woman's son when the son is not his. since the two are not related by blood.

Fatawa Rahimiyyah vol.3