Saint St Augustine:
-It is Not Impossible that Some Believers May Pass Through a Purgatorial Fire in the Future Life.
And it is not impossible that something of the same kind may take place even after this life. It is a matter that may be inquired into, and either ascertained or left doubtful, whether some believers shall pass through a kind of purgatorial fire, and in proportion as they have loved with more or less devotion the goods that perish, be less or more quickly delivered from it.
(S. Augustine, Enchiridion on Faith, Hope & Love, Chapter 69)
Written about 400AD.
Tertullian:
“A woman, after the death of her husband . . . prays for his soul and asks that he may, while waiting, find rest; and that he may share in the first resurrection. And each year, on the anniversary of his death, she offers the sacrifice”
(Monogamy 10:1–2)
Written about 216AD.