Advice to an Empress on the Treatment of Heretics

Si ergo praedicit nomen catholicum venerantur et diligunt, et inter Domini corporis volunt membra numerari, pravos errores, quos temere admiserent, detestentur, et agant poenitentiam impiarum blasphemiarum, cruentorumque factorum. Succumbant pro salute animarum suarum synodalibus, quae in civitate Chalcedonensi sunt confirmata, decretis. Et quia ad intelligendum sacramentum salutis humanae, nisi fides vera et humilitas quieta non pervenit, credant quod legunt in Evangelio, quod confitentur in symbolo, nec impiis dogmatibus misceantur. Fides enim catholica sicut damnat Nestorium, qui in uno Domino nostro Jesu Christo duas ausus est praedicare personas, ita damnat etiam Eutychen cum Dioscoro, qui ab unigenito Deo Verbo negant in utero Virginis matris veritatem carnis humanae susceptam. Si quid autem erga praedictorum conversionem exhortatio vestra profecerit, quod gloriam vobis praestabit aeteram, peto hoc mihi clementiae vestra litteris indicetis; ut et vos boni operis fructum cepisse, et illos gaudeam misericordia Domini non periisse.  Sanctus Leo Magnus, Epistola CXXIII, Ad Eudociam Augustam

Thus if the aforementioned venerate and love the Catholic name and wish to be numbered among the members of the Lord's body, let them despise the depraved errors which in recklessness they have committed, and let them make penitence for impious blasphemies and bloodshed. For the salvation of their souls let them yield to the synod's decrees which have been confirmed in the city of Chalcedon. And because the understanding of man's salvation does not come but with true faith and quiet humility, let them believe what they read in the Gospel and what they confess in the Creed, and let them not be mixed up with impious teachings. Just as the catholic faith condemns Nestorius, who dared to assert two persons in our one Lord Jesus Christ, so does it condemn Eutyches and Dioscorus who deny that the true human flesh was assumed in the womb of Virgin Mother's by the only begotten Word of God. If, then, your exhortations gain success in converting them, which will raise you to eternal glory, I ask your clemency to inform me in writing, so that I may grasp the fruit of your good work and the joy that they, through the Lord's mercy, have not perished. Pope Leo the Great, Letter 123, To the Empress Eudocia