Exodus 7:6

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

4 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.

5 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.

6 And Moses and Aaron did as the LORD commanded them, so did they.

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

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

9 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.