2 Peter 2:20-22

If they have escaped the corruption of the world by knowing our Lord and Saviour Jesus Christ and are again entangled in it and are overcome, they are worse off at the end than they were at the beginning. It 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. Of them the proverbs are true: ‘A dog returns to its vomit,’ and, ‘A sow that is washed returns to her wallowing in the mud.’