Exodus 3:2-5

2Then the angel of Adonai appeared to him in a flame of fire from within a bush. So he looked and saw the bush burning with fire, yet it was not consumed.

3Moses thought, “I will go now, and see this great sight. Why is the bush not burnt?”

4When Adonai saw that he turned to look, He called to him out of the midst of the bush and said, “Moses, Moses!” So he answered, “Hineni.”

5Then He said, “Come no closer. Take your sandals off your feet, for the place where you are standing is holy ground.”