24 Consider with what want of judgment you dare to blame those who strive for the truth against falsehood. For who ought more justly to be indignant against the other?— whether he who supports God's enemies, or he who, in opposition to him who supports God's enemies, unites with us on behalf of the truth of the Church?— except that it is plain that the ignorant are also excited and angry, because by the want of counsel and discourse they are easily turned to wrath; so that of none more than of you does divine Scripture say, “A wrathful man stirs up strifes, and a furious man heaps up sins.” For what strifes and dissensions have you stirred up throughout the churches of the whole world!
Moreover, how great sin have you heaped up for yourself, when you cut yourself off from so many flocks! For it is yourself that you have cut off. Do not deceive yourself, since he is really the schismatic who has made himself an apostate from the communion of ecclesiastical unity. For while you think that all may be excommunicated by you, you have excommunicated yourself alone from all; and not even the precepts of an apostle have been able to mould you to the rule of truth and peace, although he warned, and said, “I therefore, the prisoner of the Lord, beseech you that you walk worthy of the vocation wherewith you are called, with all lowliness and meekness, with long-suffering, forbearing one another in love; endeavouring to keep the unity of the Spirit in the bond of peace.
There is one body and one Spirit, even as you are called in one hope of your calling; one Lord, one faith, one baptism; one God and Father of all, who is above all, and through all, and in us all.”
Source: The Epistles of Cyprian (New Advent)