Exodus 3:1-5

1 Now Moses was keeping the flock of Jethro, his father-in-law, the priest of Midian, and he led the flock to the back of the wilderness, and came to God's mountain, to Horeb.  2 The angel of Yahweh appeared to him in a flame of fire out of the midst of a bush. He looked, and behold, the bush burned with fire, and the bush was not consumed.  3 Moses said, I will turn aside now, and see this great sight, why the bush is not burnt.  4 When Yahweh saw that he turned aside to see, God called to him out of the midst of the bush, and said, "Moses! Moses!"  He said, "Here I am."

5 He said, "Don't come close. Take off your sandals from off your feet, for the place you are standing on is holy ground."