Sh'mot (Exo) 7:9-10

“When Pharaoh says to you, ‘Perform a miracle,’ tell Aharon to take his staff and throw it down in front of Pharaoh, so that it can become a snake.” Moshe and Aharon went in to Pharaoh and did this, as ADONAI had ordered — Aharon threw down his staff in front of Pharaoh and his servants, and it turned into a snake.