Acts 7:29-33

Then fled Moses at this saying, and was a stranger in the land of Madian, where he begat two sons.

And when forty years were expired, there appeared to him in the wilderness of mount Sina an angel of the Lord in a flame of fire in a bush.

When Moses saw it, he wondered at the sight: and as he drew near to behold it, the voice of the Lord came unto him,

Saying, I am the God of thy fathers, the God of Abraham, and the God of Isaac, and the God of Jacob. Then Moses trembled, and durst not behold.

Then said the Lord to him, Put off thy shoes from thy feet: for the place where thou standest is holy ground.