Exodus 7:8-10

Then GOD spoke to Moses and Aaron. He said, “When Pharaoh speaks to you and says, ‘Prove yourselves. Perform a miracle,’ then tell Aaron, ‘Take your staff and throw it down in front of Pharaoh: It will turn into a snake.’” Moses and Aaron went to Pharaoh and did what GOD commanded. Aaron threw his staff down in front of Pharaoh and his servants, and it turned into a snake.