Charles Ellicott Commentary 1 Kings 19:9

"And he came thither unto a cave, and lodged there; and, behold, the word of Jehovah came to him, and he said unto him, What doest thou here, Elijah?" — 1 Kings 19:9 (ASV)

A cave. —This is properly, “the cave”—perhaps a reference to some cave already well known, as connected with the giving of the Law on Mount Sinai, or perhaps only an anticipatory reference to the cave which Elijah’s sojourn was to make famous.

The word of the Lord came to him. —The connection suggests that this message came to him in vision or dream at night. The Septuagint implies this distinctly by inserting in 1 Kings 19:11 the word “to-morrow,” which is also found in the rather vague and prosaic paraphrase of the passage in Josephus. What Elijah replies in imagination in the vision, he repeats next day in actual words.