Jamieson, Fausset and Brown on 1 Kings 18:42

42. 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 fulfilment of the promise (1Ki 18:1).

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