Exodus 3:1-3

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 the mountain of God, unto Horeb. 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.