Proverbs 26:11 in the World English Bible
As a dog that returns to his vomit, so is a fool who repeats his folly.
Context
10 The great God that formed all things both rewardeth the fool, and rewardeth transgressors.
11 As a dog returneth to his vomit, so a fool returneth to his folly.
12 Seest thou a man wise in his own conceit? there is more hope of a fool than of him.