1 Kings 18:42

So Ahab went up to eat and to drink. And Elijah went up to the top of Carmel; and he cast himself down upon the earth, and put his face between his knees,

Ahab went up to eat and to drink. Ahab, kept in painful excitement by the agonizing scene, had eaten nothing all the day. He was recommended to refresh himself without a moment's delay; and while the king was thus occupied, the prophet far from taking rest, was absorbed in prayer for the fulfillment of the promise (1 Kings 18:1).

Put his face between his knees - a posture of earnest supplication still used.