WCF 24.3.
It is lawful for all sorts of people to marry, who are able with judgment to give their consent. (Heb. 13:4, 1 Tim. 4:3, 1 Cor. 7:36–38) Yet it is the duty of Christians to marry only in the Lord. (1 Cor. 7:39) And therefore such as profess the true reformed religion should not marry with infidels, papists, or other idolaters: neither should such as are godly be unequally yoked, by marrying with such as are notoriously wicked in their life, or maintain damnable heresies. (Gen. 34:14, Exod. 34:16, Deut. 7:3–4, 1 Kings 11:4, Neh. 13:25–27, Mal. 2:11–12, 2 Cor. 6:14)