Exodus 3:2-5

And the angel of Jehovah appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed. And Moses said, I will turn aside now, and see this great sight, why the bush is not burnt. And when Jehovah saw that he turned aside to see, God called unto him out of the midst of the bush, and said, Moses, Moses. And he said, Here am I. And he said, Draw not nigh hither: put off thy shoes from off thy feet, for the place whereon thou standest is holy ground.