2 Samuel 18:5-7

The king commanded Joab and Abishai and Ittai, saying, “Deal gently with the young man Absalom for my sake.” And all the men heard when the king gave orders to all the commanders about Absalom. So the men went out into the field against Israel, and the battle was fought in the forest of Ephraim. The men of Israel [who supported Absalom] were defeated there by the men of David, and a great slaughter took place there that day, 20,000 men.