Exodus 7:9-10

“When Pharaoh shall speak to you, saying, ‘Show a miracle,’ then you shall say to Aaron, ‘Take your rod, and throw it before Pharaoh,’ and it shall become a serpent.” So Moses and Aaron went to Pharaoh, and they did what the LORD had commanded. And Aaron threw down his rod before Pharaoh and before his servants, and it became a serpent.