Nicene and Post-Nicene Fathers, Vol. IV:
Writings in Connection with the Manichæan Controversy.: Chapter 38

Chapter 38.—Eternal Fire Torturing the Wicked, Not Evil.

For neither is eternal fire itself, which is to torture the impious, an evil nature, since it has its measure, its form and its order depraved by no iniquity; but it is an evil torture for the damned, to whose sins it is due.  For neither is yonder light, because it tortures the blear-eyed, an evil nature.