on Purgatory

Clement of Alexandria, Stromata Book 6 ch 14 (150-215 ad)
Accordingly the believer, through great discipline, divesting himself of the passions, passes to the mansion which is better than the former one, viz., to the greatest torment, taking with him the characteristic of repentance from the sins he has committed after baptism. He is tortured then still more--not yet or not quite attaining what he sees others to have acquired. Besides, he is also ashamed of his transgressions. The greatest torments, indeed, are assigned to the believer. For God's righteousness is good, and His goodness is righteous. And though the punishments cease in the course of the completion of the expiation and purification of each one, yet those have very great and permanent grief who are found worthy of the other fold, on account of not being along with those that have been glorified through righteousness.