2 Samuel 17:14, 23

Then Absalom and all the men of Israel said, “The counsel of Hushai the Archite is better than the counsel of Ahithophel.” For the LORD had ordained to thwart the good counsel of Ahithophel, so that the LORD might bring calamity on Absalom.

Now when Ahithophel saw that his counsel was not followed, he saddled his donkey and arose and went to his home, to his city, and set his house in order, and strangled himself; thus he died and was buried in the grave of his father.