II. The bishops of Italy must not allow those Manichæans who have quitted the city to escape or lie concealed.
And because we know that a good many of those who are involved here in too close an accusation for them to clear themselves have escaped, we have sent this letter to you, beloved, by our acolyth: that your holiness, dear brothers, may be informed of this, and see fit to act with diligence and caution, lest the men of the Manichæan error be able to find opportunity of hurting your people and of teaching their impious doctrines. For we cannot otherwise rule those entrusted to us unless we pursue with the zeal of faith in the Lord those who are destroyers and destroyed: and with what severity we can bring to bear, cut them off from intercourse with sound minds, lest this pestilence spread much wider.
Wherefore I exhort you, beloved, I beseech and warn you to use such watchful diligence as you ought and can employ in tracking them out, lest they find opportunity of concealment anywhere. For as he will have a due recompense of reward from God, who carries out what conduces to the health of the people committed to him; so before the Lord's judgment-seat no one will be able to excuse himself from a charge of carelessness who has not been willing to guard his people against the propagators of an impious misbelief. Dated 30 January, in the consulship of the illustrious Theodosius Augustus (18th time) and Albinus (444).
Source: Letters (New Advent)