2 Peter 2:21-22

21It would have been better for them not to have known the way of righteousness, than to have known it and then to turn their backs on the sacred command that was passed on to them. 22Of them the proverbs are true: “A dog returns to its vomit,” Prov. 26:11 and, “A sow that is washed returns to her wallowing in the mud.”