1 Corinthians 7:12-14

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. For the unbelieving husband is sanctified [that is, he receives the blessings granted] through his [Christian] wife, and the unbelieving wife is sanctified through her believing husband. Otherwise your children would be [ceremonially] unclean, but as it is they are holy.