I Samuel 24:3, 8

So he came to the sheepfolds by the road, where there was a cave; and Saul went in to attend to his needs. (David and his men were staying in the recesses of the cave.)

David also arose afterward, went out of the cave, and called out to Saul, saying, “My lord the king!” And when Saul looked behind him, David stooped with his face to the earth, and bowed down.