2 Peter 2:22

In their case is seen the truth of the proverb-- 'A dog returns to what he has vomited' and 'A sow after washing to her wallowing-place in the mud.'

Matthew 12:45

Then it goes and brings with it seven other spirits more wicked than itself, and they go in, and make their home there; and the last state of that man proves to be worse than the first. So, too, will it be with this 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 it goes and brings with it seven other spirits more wicked than itself, and they go in, and make their home there; and the last state of that man proves to be worse than the first. So, too, will it be with this wicked generation."
2 Peter 2:22
In their case is seen the truth of the proverb-- 'A dog returns to what he has vomited' and 'A sow after washing to her wallowing-place in the mud.'