What is the ruling on committing adultery with a woman who is ceremonially (urfi) married, and what are the implications of her pregnancy with the father being unknown, and is it permissible for the adulterer to marry her after his repentance?

Adultery is one of the gravest sins. If the adulterer is married, the sin is even greater, and the transgression increases if the woman with whom adultery was committed is also married. One must immediately repent from this sin. As for the child conceived, it is attributed to the man the mother is married to, provided that their marriage is one that legally attributes children to him. It is not permissible to marry her as long as she is married. One can marry her after her husband divorces her and her waiting period ('iddah) ends, on condition that both of them repent from adultery.