Exodus 3:2-5

The Angel of the LORD appeared to him in a blazing flame of fire from the midst of a bush; and he looked, and behold, the bush was on fire, yet it was not consumed. So Moses said, “I must turn away [from the flock] and see this great sight—why the bush is not burned up.” When the LORD saw that he turned away [from the flock] to look, God called to him from the midst of the bush and said, “Moses, Moses!” And he said, “Here I am.” Then God said, “Do not come near; take your sandals off your feet [out of respect], because the place on which you are standing is holy ground.”