Yenra : Catholic Prayers : Venom of Heretics

Do not, even for the sake of defending the faith, converse with heretics, for fear less their words instill their venom into thy mind. If thou meet with a book said to be by one of the heretics, read it not, lest it fill thy heart with deadly poison; but so continue in that doctrine which thou hast learnt in holy church, as neither to add or to take from it.

Isaias, Abbot [4th Cent.]