St. Augustine on the Faithful Departed saved through a Certain Purgatorial Fire

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.

St. Augustine – Handbook on Faith, Hope, and Charity – c. 421 A.D.

St. Augustine on Purgatory, Prayers for the Departed, & the Sacrifice of the Mass

There is an ecclesiastical discipline, as the faithful know, when the names of the martyrs are read aloud in that place at the altar of God, where prayer is not offered for them. Prayer, however, is offered for other dead who are remembered. It is wrong to pray for a martyr, to whose prayers we ought ourselves be commended. But by the prayers of the Holy Church, and by the salvific sacrifice, and by the alms which are given for their spirits, there is no doubt that the dead are aided, that the Lord might deal more mercifully with them than their sins would deserve. The whole Church observes this practice which was handed down by the Fathers: that it prays for those who have died in the communion of the Body and Blood of Christ, when they are commemorated in their own place in the sacrifice itself; and the sacrifice is offered also in memory of them, on their behalf. If, then, works of mercy are celebrated for the sake of those who are being remembered, who would hesitate to recommend them, on whose behalf prayers to God are not offered in vain? It is not at all to be doubted that such prayers are of profit to the dead; but for such of them as lived before their death in a way that makes it possible for these things to be useful to them after death.

St. Augustine – Sermons – c. 411 A.D.

St. Augustine on Purgatory and Temporal Punishment of Sin

Temporal punishments are suffered by some in this life only, by some after death, by ‘some both here and hereafter, but all of them before that last and strictest judgment. But not all who suffer temporal punishments after death will come to eternal punishments, which are to follow after that judgment.

St. Augustine – City of God – A.D. 419