Exodus 7:9-10

“When Pharaoh speaks to you, saying, ‘Perform a miracle!’ then you shall tell Aaron, ‘Take your rod, and cast it down before Pharaoh, and it will become a serpent.’” Moses and Aaron went in to Pharaoh, and they did so, as Yahweh had commanded. Aaron cast down his rod before Pharaoh and before his servants, and it became a serpent.