Luke 15:15-16

So he went and joined himself to a citizen of that country, who sent him into his fields to feed swine.

2 Peter 2:22

It has happened to them according to the true proverb, "A dog turns back to its own vomit," and, "A sow, after having washed, returns to wallowing in the mire."

Treasury of Scripture Knowledge

Summary

And the swine, because it divideth the hoof, yet cheweth not the cud, it is unclean unto you: ye shall not eat of their flesh, nor touch their dead carcase.

Bible References

The swine

Luke 15:15
So he went and joined himself to a citizen of that country, who sent him into his fields to feed swine.
2 Peter 2:22
It has happened to them according to the true proverb, "A dog turns back to its own vomit," and, "A sow, after having washed, returns to wallowing in the mire."