That marriage is not to be contracted with Gentiles
In Tobias: “Take a wife from the seed of your parents, and take not a strange woman who is not of the tribe of your parents.” Also in Genesis, Abraham sends his servant to take from his seed Rebecca, for his son Isaac. Also in Esdras, it was not sufficient for God when the Jews were laid waste, unless they forsook their foreign wives, with the children also whom they had begotten of them. Also in the first Epistle of Paul to the Corinthians: “The woman is bound so long as her husband lives; but if he die, she is freed to marry whom she will, only in the Lord.
But she will be happier if she abide thus.” And again: “Do you not know that your bodies are the members of Christ? Shall I take the members of Christ, and make them the members of an harlot? Far be it from me. Or do you not know that he who is joined together with an harlot is one body? For two shall be in one flesh. But he who is joined to the Lord is one spirit.” Also in the second to the Corinthians: “Be not joined together with unbelievers. For what participation is there between righteousness and unrighteousness? Or what communication has light with darkness?” Also concerning Solomon in the third book of Kings: “And foreign wives turned away his heart after their gods.”
Source: The Treatises of Cyprian (New Advent)