1 Corinthians 7:12-14

Now, I will speak to the rest of you, though I do not have a direct command from the Lord. If a fellow believer has a wife who is not a believer and she is willing to continue living with him, he must not leave her. And if a believing woman has a husband who is not a believer and he is willing to continue living with her, she must not leave him. For the believing wife brings holiness to her marriage, and the believing husband brings holiness to his marriage. Otherwise, your children would not be holy, but now they are holy.