Exodus 3:1 - 6
ESV - 1 Now Moses was keeping the flock of his father-in-law, Jethro, the priest of Midian, and he led his flock to the west side of the wilderness and came to Horeb, the mountain of God. 2 And the angel of the Lord appeared to him in a flame of fire out of the midst of a bush. He looked, and behold, the bush was burning, yet it was not consumed.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.