What is the ruling on a wife who combines two husbands at one time, one marriage contract being legitimate and the other customary?

This wife and the man who entered into an urfi contract with her have committed a grave sin. Adultery is a great indecency, and its ugliness increases if the woman is married, as it is considered a betrayal of her husband. Marrying a married woman is pure fornication if the contracting party knows of her marriage. The perpetrator deserves a hundred lashes and a year of exile if he is not muhsan (chaste), and stoning to death if he is muhsan. The adulterous married woman is not forbidden to her husband except by lian (oath of condemnation). If lian occurs between them, she becomes permanently forbidden to him.