Hebrews 10:38
“Now the just” (he says) “shall live by faith, but if any man draw back, My soul shall have no pleasure in him.” This is a great encouragement when one shows that they have succeeded in the whole matter and are losing it through a little indolence. “But we are not of them that draw back unto perdition, but of them that believe to the saving of the soul.”
Source: Homilies on the Epistle to the Hebrews (New Advent)