Exodus 7:8-10
The LORD said to Moses and Aaron,
"When Pharaoh says to you, 'Perform a miracle,' then say to Aaron, 'Take your staff and throw it down before Pharaoh,' and it will become a snake."
So Moses and Aaron went to Pharaoh and did just as the LORD commanded. Aaron threw his staff down in front of Pharaoh and his officials, and it became a snake.