1 Corinthians 7:11-13

(but even if she does leave him, let her remain single or else be reconciled to her husband) and that the husband should not leave his wife. To the rest I declare—I, not the Lord [since Jesus did not discuss this]—that if any [believing] brother has a wife who does not believe [in Christ], and she consents to live with him, he must not leave her. And if any [believing] woman has an unbelieving husband, and he consents to live with her, she must not leave him.