2 Peter 2:22

Their case is that described in the true proverb, "A dog returns to what he has vomited," and also in the other proverb, "The sow has washed itself and now goes back to roll in its filth."

Matthew 12:45

Then he goes and brings back with him seven other spirits more wicked than himself, and they come in and dwell there; and in the end that man's condition becomes worse than it was at first. So will it be also with the present wicked generation."

Treasury of Scripture Knowledge

Summary

As a dog returneth to his vomit, so a fool returneth to his folly.

Bible References

A dog

Matthew 12:45
Then he goes and brings back with him seven other spirits more wicked than himself, and they come in and dwell there; and in the end that man's condition becomes worse than it was at first. So will it be also with the present wicked generation."
2 Peter 2:22
Their case is that described in the true proverb, "A dog returns to what he has vomited," and also in the other proverb, "The sow has washed itself and now goes back to roll in its filth."