Exodus 7:9-10
Exodus 7:9-10 RSV
“When Pharaoh says to you, ‘Prove yourselves by working a miracle,’ then you shall say to Aaron, ‘Take your rod and cast it down before Pharaoh, that it may become a serpent.’ ” So Moses and Aaron went to Pharaoh and did as the LORD commanded; Aaron cast down his rod before Pharaoh and his servants, and it became a serpent.