1 Corinthians 7:15-16:

But if the unbelieving depart, let him depart. A brother or a sister is not under bondage in such cases: but God hath called us to peace.
For what knowest thou, O wife, whether thou shalt save thy husband? or how knowest thou, O man, whether thou shalt save thy wife?

See also:

God’s Blessing on Your Kids
Can I Believe and Receive a Healing for Someone Else?