Epiphanius relates the following (
Panarion 30.24):
And again, when St. John himself was preaching in Asia, it is reported that he did an extraordinary thing as an example of the truth. Although his way of life was most admirable and appropriate to his apostolic Holy Spirit who said, “Look what is at the bath!” (2) To his companions’ surprise he actually went to the bathing-room, approached the attendant who took the bathers’ clothes, and asked who was inside in the bathingroom. (3) And the attendant stationed there to watch the clothes—some people do this for a living in the gymnasia—said to St. John, “Ebion is inside.” (4) But John understood at once why the Holy Spirit’s guidance had impelled him to approach the bath, as I said—as a memorial to leave us the truth’s advice as to who Christ’s servants and apostles are, and the sons of that same truth, but what the vessels of the evil one are, and the gates of hell; though these cannot prevail against the rock, and God’s holy church which is founded on it. (5) Becoming disturbed at once and crying out John said in an aside audible to all—as a testimony in evidence of undefiled doctrine—“Let’s get out of here in a hurry, brothers, or the bath may fall and bury us along with the person who is inside in the bathingroom, Ebion, because of his impiety.” (6) And no one need be surprised to hear that Ebion met John. The blessed John had a very long life, and survived till the reign of Trajan.71 (7) But anyone can see that all the apostles distinguished Ebion’s faith (from their own), and considered it foreign to the character of their preaching.
Irenaeus tells this story instead (A.H. 3.3.4):
There are also those who heard from him [Polycarp] that John, the disciple of the Lord, going to bathe at Ephesus, and perceiving Cerinthus within, rushed out of the bath-house without bathing, exclaiming, “Let us flee, lest even the bath-house fall down, because Cerinthus, the enemy of the truth, is within.
It is widely acknowledged that "Ebion" is a fiction. The name derives from a need of heresiologists to trace the origin of each heresy to a named founder, thereby discrediting their doctrine by ascribing it to a deviant teacher. As late as the fourth century, Eusebius is able to describe such a group without deriving the etymology from the name of a founder:
The ancients quite properly called these men Ebionites, because they held poor and mean opinions concerning Christ.
Epiphanius also shows that he knows of their own claimed etymology and denies it (
Panarion 30.16):
They themselves, if you please, boastfully claim that they are poor because they sold their possessions in the apostles’ time and laid them at the apostles’ feet, and went over to a life of poverty and renunciation; and thus, they say, they are called “poor” by everyone. But there is no truth to this claim of theirs either; he was really named Ebion. I suppose the poor wretch was named prophetically by his father and mother.
And the stories quoted also show that Ebion and Cerinthus were considered in very similar terms, as the opponent of John, said to have written the fourth gospel, so much so that the same story can find itself applied to both names. The origin of this story need nothing more than the idea that John would have opposed the view of Jesus as a "mere man." Irenaeus isn't even bold enough to claim that he had heard the story from Polycarp, only that he had heard the story in circulation and that it had come to be attributed to Polycarp. And yet that attribution itself doesn't need anything more than the idea that Polycarp was the hearer of John. The whole thing disappears into a fog of rumors.
And yet it's less often shown that Cerinthus is also a fiction, created for much the same reasons as Ebion. Recently, I think I came across the origin of the fictitious name. Recall that the "Gospel of the Ebionites" (called the Gospel according to Matthew) was used by those who, among other things, are attributed with vegetarianism and a rejection of sacrifices. And Epiphanius quotes from this text as follows (
Panarion 30.12):
And, “John came baptizing, and there went out unto him Pharisees and were baptized, and all Jerusalem. And John had a garment of camel’s hair, and a girdle of skin about his loins. And his meat,” it says, “was wild honey, whose taste was the taste of manna, as a cake in oil.” This, if you please, to turn the account of the truth into falsehood, and substitute “a cake in honey” for “locusts”!
Note that it is often said that this alleged substitution of "pancakes" (
egkrides) for "locusts" (
akrides) shows that the text was Greek instead of Hebrew.
This story comes near the beginning of the text, with the story of John and his relationship to Jesus (also at the start of canonical Mark and John), and touches on one of the most controversial points about the people using the text, their rejection of meat in favor of a form of vegetarianism. So the text is highly visible and peculiar to those who oppose them (much like the famous opening of the Gospel used by Marcion).
And so it would be no surprise if this text gave rise to polemical use, much like it does in Epiphanius. The word "Cerinthus" in Greek means "bee-bread," a waxy substance believed to be the sustenance of bees:
https://www.jstor.org/stable/283989
So when the text talks about eating honey, as though shaped into a pancake, what could be more appropriate as a way to taunt them but to call them the followers of a certain "bee-bread" man? Such is the fictitious Cerinthus.