Proverbs 26:11
As a dog returns to his vomit, so a fool returns to his folly.
Torrey's Topical Textbook—AKJV

Matthew 7:6
Give not that which is holy to the dogs, neither cast you your pearls before swine, lest they trample them under their feet, and turn again and rend you.
Torrey's Topical Textbook—AKJV

2 Peter 2:22
But it is happened to them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.
Torrey's Topical Textbook—AKJV