Albert Barnes Commentary 1 Kings 18:42

"So Ahab went up to eat and to drink. And Elijah went up to the top of Carmel; and he bowed himself down upon the earth, and put his face between his knees." — 1 Kings 18:42 (ASV)

Ahab could feast; Elijah could not, or would not.

Ascending Mount Carmel not quite to the highest elevation (1 Kings 18:43), but to a point a little below it from where the sea was not visible, he proceeded to pray earnestly for rain, just as he had formerly prayed that it would not rain.