Shemoth (Exodus) 7:9-10

When Pharaoh speaks to you, saying, ‘Show a miracle for yourselves,’ then you shall say to Aharon, ‘Take your rod and throw it before Pharaoh, and let it become a serpent.’ So Mosheh and Aharon went in to Pharaoh, and they did so, as יהוה commanded. And Aharon threw his rod before Pharaoh and before his servants, and it became a serpent.