Charles Ellicott Commentary 1 Samuel 23:2

"Therefore David inquired of Jehovah, saying, Shall I go and smite these Philistines? And Jehovah said unto David, Go, and smite the Philistines, and save Keilah." — 1 Samuel 23:2 (ASV)

David inquired of the Lord. —The inquiry was not made of the priest wearing the ephod, by means of the Urim and Thummim, for, according to 1 Samuel 23:6, Abiathar, the high priest who succeeded the murdered Ahimelech, only joined David at Keilah, the citizens of which place were then asking for his aid against their enemies. But Gad the prophet was with David, and the inquiry was made, no doubt, through him.

We know that such inquiries were made through prophets, for we possess a detailed account of such an inquiry being made by Jehoshaphat of the prophet Micaiah (1 Kings 22:5; 1 Kings 22:7–8), in which passage the same formula is used as in this case. The Talmud too, when discussing the inquiries made through the Urim and Thummim, while dwelling on the greater weight of the decision pronounced by the sacred stones, assumes that questions were also asked through the prophets. “The decree pronounced by a prophet is revocable, but the decision of the Urim and Thummim is irrevocable.”—Treatise Yoma, fol. 73 Colossians 1:0.