1 Corinthians 7:15

If the unbelieving husband or the unbelieving wife will leave his or her correlate, that is, so leave them as to return no more to live as a husband or as a wife with her or him that is Christian, let him depart. Such a person hath broken the bond of marriage, and in such cases Christians are not under bondage, they are not tied by law to fetch them again, nor by the laws of God to keep themselves unmarried for their perverseness. But it may be objected, that nothing but adultery, by the Divine law, breaketh that bond. Answer. That is denied. Nothing but adultery is a justifiable cause of divorce: no man may put away his wife, nor any wife put away her husband, but for adultery. But the husband's voluntary leaving his wife, or the wife's voluntary leaving her husband, with a resolution to return no more to them, breaks also the bond of marriage, frustrating it as to the ends for which God hath appointed it; and, after all due means used to bring again the party departing to their duty, doth certainly free the correlate. So that although nothing can justify repudiation, or putting away a wife or a husband, and marrying another, but the adultery of the person so divorced and repudiated; yet the departure either of husband or wife without the other's consent for a long time, and refusal to return after all due means used, especially if the party so going away doth it out of a hatred and abomination of the other's religion, will justify the persons so deserted, after due waiting and use of means to reduce him or her to their duty, wholly to cast off the person deserting; for no Christian in such a case, by God's law, is under bondage. But God hath called us to peace; for God hath called Christians unto peace, and in his ordinance of marriage aimed at the quiet and peace of his people in their service of him in their families and relations; and therefore as Christians ought not to disturb the peace of their own consciences, turning away their relations, though they be unbelievers; yet neither are they bound, if such will leave them, to court their own continual trouble and disturbance.