'Unbelieving' in the Bible

And a woman who has an unbelieving husband--if he consents to live with her, let her not separate from him.

For, in such cases, the unbelieving husband has become--and is--holy through union with a Christian woman, and the unbelieving wife is holy through union with a Christian brother. Otherwise your children would be unholy, but in reality they have a place among God's people.