'Believer' in the Bible

To the rest I say -- I, not the Lord -- if a brother has a wife who is not a believer and she is happy to live with him, he should not divorce her.

And if a woman has a husband who is not a believer and he is happy to live with her, she should not divorce him.

For if any one were to see you, who know the real truth of this matter, reclining at table in an idol's temple, would not his conscience (supposing him to be a weak believer)

Why, your knowledge becomes the ruin of the weak believer--your brother, for whom Christ died!

Have we no right to lead about a wife that is a believer, even as the rest of the apostles, and the brethren of the Lord, and Cephas?