3 Now, since there exists, according to them, also something else which they declare to be outside of the Pleroma, into which they further hold there descended that higher power who went astray, it is in every way necessary that the Pleroma either contains that which is beyond, yet is contained (for otherwise, it will not be beyond the Pleroma; for if there is anything beyond the Pleroma, there will be a Pleroma within this very Pleroma which they declare to be outside of the Pleroma, and the Pleroma will be contained by that which is beyond: and with the Pleroma is understood also the first God); or, again, they must be an infinite distance separated from each other — the Pleroma [I mean], and that which is beyond it.
But if they maintain this, there will then be a third kind of existence, which separates by immensity the Pleroma and that which is beyond it. This third kind of existence will therefore bound and contain both the others, and will be greater both than the Pleroma, and than that which is beyond it, inasmuch as it contains both in its bosom. In this way, talk might go on for ever concerning those things which are contained, and those which contain. For if this third existence has its beginning above, and its end beneath, there is an absolute necessity that it be also bounded on the sides, either beginning or ceasing at certain other points, [where new existences begin.] These, again, and others which are above and below, will have their beginnings at certain other points, and so on ad infinitum; so that their thoughts would never rest in one God, but, in consequence of seeking after more than exists, would wander away to that which has no existence, and depart from the true God.
Source: Adversus haereses (New Advent)