Exodus 7:6

3 And I will make Pharaoh's heart hard, and my signs and wonders will be increased in the land of Egypt.

4 But Pharaoh will not give ear to you, and I will put my hand on Egypt, and take my armies, my people, the children of Israel, out of Egypt, after great punishments.

5 And the Egyptians will see that I am the Lord, when my hand is stretched out over Egypt, and I take the children of Israel out from among them.

6 And Moses and Aaron did so: as the Lord gave them orders, so they did.

7 And Moses was eighty years old, and Aaron eighty-three years old, when they gave the Lord's word to Pharaoh.

8 And the Lord said to Moses and Aaron,

9 If Pharaoh says to you, Let me see a wonder: then say to Aaron, Take your rod and put it down on the earth before Pharaoh so that it may become a snake.