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

Proverbs 27:22
Though you should bray a fool in a mortar among wheat with a pestle, yet will not his foolishness depart from him.
Torrey's Topical Textbook—AKJV