Exodus 7:9-10

“When Pharaoh says to you, ‘Work a miracle [to prove your authority],’ then you say to Aaron, ‘Take your staff and throw it down before Pharaoh, so that it may become a serpent.’ ” So Moses and Aaron came to Pharaoh, and did just as the LORD had commanded; Aaron threw down his staff before Pharaoh and his servants, and it became a serpent.