Exodus 7:6

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

But Pharaoh will not listen to you, so I will lay my hand on Egypt, and bring out my armies, my people the children of Israel, out of the land of Egypt by great judgments.

The Egyptians shall know that I am the LORD when I stretch out my hand on Egypt, and bring the children of Israel out from among them.”

Moses was eighty years old, and Aaron eighty-three years old, when they spoke to Pharaoh.

The LORD spoke to Moses and to Aaron, saying,

“When Pharaoh speaks to you, saying, ‘Perform a miracle!’ then you shall tell Aaron, ‘Take your rod, and cast it down before Pharaoh, and it will become a serpent.’”