Hence it is [supposed] that schisms seldom happen among heretics, because, even when they exist, they are not obvious. Their very unity, however, is schism. I am greatly in error if they do not amongst themselves swerve even from their own regulations, forasmuch as every man, just as it suits his own temper, modifies the traditions he has received after the same fashion as the man who handed them down did, when he moulded them according to his own will. The progress of the matter is an acknowledgment at once of its character and of the manner of its birth. That was allowable to the Valentinians which had been allowed to Valentinus; that was also fair for the Marcionites which had been done by Marcion—even to innovate on the faith, as was agreeable to their own pleasure. In short, all heresies, when thoroughly looked into, are detected harboring dissent in many particulars even from their own founders. The majority of them have not even churches. Motherless, houseless, creedless, outcasts, they wander about in their own essential worthlessness.
Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XLII