Exodus 4:1-3

And Moses answered and said, But, behold, they will not believe me, nor hearken unto my voice: for they will say, The LORD hath not appeared unto thee.

And the LORD said unto him, What is that in thine hand? And he said, A rod.

And he said, Cast it on the ground. And he cast it on the ground, and it became a serpent; and Moses fled from before it.