Tradition
St. Clement of Alexandria
The Stromata, or Miscellanies
Book 7 › Chapter 6 · Part 2 of 2
Prayers and Praise from a Pure Mind, Ceaselessly Offered, Far Better Than Sacrifices
But we say that the fire sanctifies not flesh, but sinful souls; meaning not the all-devouring vulgar fire but that of wisdom, which pervades the soul passing through the fire.
Source: The Stromata, or Miscellanies (New Advent)