Sunday morning ping
It looks like Sungenis is referring to the nature of it, not the existence of it.
Not the word purgatory per se, but certainly a description of a purgatorial fire. Here are the words of St Augustine (I'm sure there are others):
"That there should be some fire even after this life is not incredible, and it can be inquired into and either be discovered or left hidden whether some of the faithful may be saved, some more slowly and some more quickly in the greater or lesser degree in which they loved the good things that perish, through a certain purgatorial fire" (Handbook on Faith, Hope, and Charity 18:69 [A.D. 421]).