Library Ignatius of Antioch Epistles (Middle Recension)
Trallians, Chapter 6: Abstain from the poison of heretics
I therefore, yet not I, but the love of Jesus Christ, entreat you that you use Christian nourishment only, and abstain from herbage of a different kind; I mean heresy. For those [that are given to this] mix up Jesus Christ with their own poison, speaking things which are unworthy of credit, like those who administer a deadly drug in sweet wine, which he who is ignorant of does greedily take, with a fatal pleasure leading to his own death.
English translation in Ante-Nicene Fathers, Vol. I (eds. Alexander Roberts and James Donaldson; Buffalo: Christian Literature Publishing Co., 1885). Public domain. Digital text via New Advent Church Fathers. ANF prints the shorter Greek (middle) recension.