What is the ruling on a Muslim man marrying a Christian woman who became pregnant through adultery by someone else?

This marriage is invalid because it took place during her iddah (waiting period) while she was pregnant from zina (unlawful sexual intercourse). He must separate from her immediately and repent to Allah. It is not permissible to marry women from the People of the Book unless they are chaste and not taking secret lovers. If her iddah ends, she gives birth, and becomes righteous, then it would be permissible for him to marry her with a new contract according to some scholars, while others prohibited it. We do not advise marrying her as long as she is not chaste.