Exodus 7:8-10

The LORD said to Moses and Aaron, “When Pharaoh tells you, ‘Perform a miracle,’ tell Aaron, ‘Take your staff and throw it down before Pharaoh. It will become a serpent.’” So Moses and Aaron went in to Pharaoh and did just as the LORD had commanded. Aaron threw down his staff before Pharaoh and his officials, and it became a serpent.