Exodus 4:3

and Aaron spoke all the words which Yahweh had spoken to Moses. He then did the signs in the sight of the people.

So Moses and Aaron came to Pharaoh, and thus they did just as Yahweh had commanded; and Aaron threw his staff down before Pharaoh and his servants, and it became a serpent.

“Go to Pharaoh in the morning as he is going out to the water, and station yourself to meet him on the bank of the Nile; and you shall take in your hand the staff that was turned into a serpent.

Then he gave a miraculous sign the same day, saying, “This is the miraculous sign which Yahweh has spoken, ‘Behold, the altar shall be torn apart and the ashes which are on it shall be poured out.’”