2 Peter 2:22

Repentance consists in no longer doing the same things, for he who reverts to the same sins is like a dog returning to his vomit.

But it has happened to them according to the true proverb: A dog returns to its own vomit, and a pig, having washed, to her rolling in the mud. For since a dog returns to its own vomit is more abominable. For what nature had hated, and thus had compelled it to reject, this again having in delight, and as if eating those things that corrupt, and as if ejected through a miscarriage of nature, is more abominable. And the pig again seeking to roll in the mud, if it does this, will appear dirtier than the previous filth.

For the truth of the proverb happened to them: The dog returns to its vomit, etc. He says this is a true proverb because he takes testimony from the Proverbs of Solomon, which is placed there with explanation: As a dog, he says, which returns to its vomit, so is a fool who repeats his foolishness (Prov. XXVI). And he added from his own: And the sow that was washed returns to wallowing in the mire. Therefore, when a dog vomits, it certainly expels the food that weighed down its chest. But when it returns to the vomit, it is again burdened by what it had been relieved of. And those who lament their sins certainly confess and cast away the evil which had satiated them wrongly and weighed down their innermost thoughts; when they repeat it after confession, they take it up again. But the sow, when washed in the mire, is rendered filthier. And he who laments his sins but does not forsake them subjects himself to greater punishment because he scorns the very pardon which he could have obtained by weeping, and he wallows in muddy water as it were, because by his tears he withdraws the cleanliness of life, and before the eyes of God even those very tears become filthy.