2 Peter 2:20-22

If they’ve escaped from the slum of sin by experiencing our Master and Savior, Jesus Christ, and then slid back into that same old life again, they’re worse than if they had never left. Better not to have started out on the straight road to God than to start out and then turn back, repudiating the experience and the holy command. They prove the point of the proverbs, “A dog goes back to its own vomit” and “A scrubbed-up pig heads for the mud.”