Exodus 7:6 (KJV)

And the LORD said unto Moses, See, I have made thee a god to Pharaoh: and Aaron thy brother shall be thy prophet.

Thou shalt speak all that I command thee: and Aaron thy brother shall speak unto Pharaoh, that he send the children of Israel out of his land.

And I will harden Pharaoh's heart, and multiply my signs and my wonders in the land of Egypt.

But Pharaoh shall not hearken unto you, that I may lay my hand upon Egypt, and bring forth mine armies, and my people the children of Israel, out of the land of Egypt by great judgments.

And the Egyptians shall know that I am the LORD, when I stretch forth mine hand upon Egypt, and bring out the children of Israel from among them.

And Moses was fourscore years old, and Aaron fourscore and three years old, when they spake unto Pharaoh.

And the LORD spake unto Moses and unto Aaron, saying,

When Pharaoh shall speak unto you, saying, Shew a miracle for you: then thou shalt say unto Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent.

And Moses and Aaron went in unto Pharaoh, and they did so as the LORD had commanded: and Aaron cast down his rod before Pharaoh, and before his servants, and it became a serpent.

Then Pharaoh also called the wise men and the sorcerers: now the magicians of Egypt, they also did in like manner with their enchantments.