That believers who differ among themselves ought not to refer to a Gentile judge
In the first Epistle of Paul to the Corinthians: “Dares any of you, having a matter against other, to discuss it among the unrighteous, and not among the saints? Do you not know that the saints shall judge this world?” And again: “Now indeed there is altogether a fault among you, because you have judgments one against another. Why do you not rather suffer injury? Or wherefore are you not rather defrauded? But you do wrong, and defraud, and this your brethren. Do you not know that the unrighteous shall not obtain the kingdom of God?”
Source: The Treatises of Cyprian (New Advent)