Exodus 7:9-10

“When Pharaoh speaks to you, saying, ‘Work a miracle,’ then you shall say to Aaron, ‘Take your staff and throw it down before Pharaoh, that it may become a serpent.’ ” So Moses and Aaron came to Pharaoh, and thus they did just as the LORD had commanded; and Aaron threw his staff down before Pharaoh and his servants, and it became a serpent.