What is the ruling on a man marrying a woman with whom his father had sexual relations?

The father has become bound by his work. Adultery is one of the gravest sins, and its prohibition intensifies if it is committed with a woman who is a prohibited degree of relation (mahram). Those who commit grave sins are subject to Allah's will. The marriage to the woman is valid, and there is no objection to it, provided she repents if she was compliant in this sin.