c. 198–206 · Tertullian, To His Wife (Ad uxorem) 2.2
Therefore, when in these days a certain woman removed her marriage from the pale of the Church, and united herself to a Gentile, and when I remembered that this had in days gone by been done by others: wondering at either their own waywardness or else the double-dealing of their advisers, in that there is no scripture which holds forth a licence of this deed,—“I wonder,” said I, “whether they flatter themselves on the ground of that passage of the first (Epistle) to the Corinthians, where it is written: If any of the brethren has an unbelieving wife, and she consents to the matrimony, let him not dismiss her; similarly, let not a believing woman, married to an unbeliever, if she finds her husband agreeable (to their continued union), dismiss him: for the unbelieving husband is sanctified by the believing wife, and the unbelieving wife by the believing husband; else were your children unclean.” It may be that, by understanding generally this monition regarding married believers, they think that licence is granted (thereby) to marry even unbelievers. God forbid that he who thus interprets (the passage) be wittingly ensnaring himself! But it is manifest that this scripture points to those believers who may have been found by the grace of God in (the state of) Gentile matrimony; according to the words themselves: “If,” it says, “any believer has an unbelieving wife;” it does not say, “takes an unbelieving wife.”