That a schism must not be made, even although he who withdraws should remain in one faith, and in the same tradition
In Ecclesiasticus, in Solomon: “He that cleaves firewood shall be endangered by it if the iron shall fall off.” Also in Exodus: “In one house shall it be eaten: you shall not cast forth the flesh abroad out of the house.” Also in the cxxxiid Psalm: “Behold how good and how pleasant a thing it is that brethren should dwell in unity!” Also in the Gospel according to Matthew: “He that is not with me is against me; and he that gathers not with me scatters.” Also in the first Epistle of Paul to the Corinthians: “But I beseech you, brethren, by the name of our Lord Jesus Christ, that you all say the same thing, and that there be no schisms among you; but that you be all joined together in the same mind and in the same opinion.” Also in the sixty-seventh Psalm: “God, who makes men to dwell with one mind in a house.”
Source: The Treatises of Cyprian (New Advent)