2 Samuel 17:14, 23

Then Absalom and all the men of Israel said, “Hushai’s advice is better than Ahithophel’s.” For the LORD had determined to defeat the counsel of Ahithophel, which really was the better plan, so that he could bring disaster on Absalom!

When Ahithophel realized that his advice had not been followed, he saddled his donkey, went to his hometown, set his affairs in order, and hanged himself. He died there and was buried in the family tomb.