Exodus 7:13
“And he hardened Pharaoh’s heart, that he hearkened not unto them; as the Lord had said.”
Then Pharaoh also called the wise men and the sorcerers: now the magicians of Egypt, they also did in like manner with their enchantments.
For they cast down every man his rod, and they became serpents: but Aaron’s rod swallowed up their rods.
And he hardened Pharaoh’s heart, that he hearkened not unto them; as the Lord had said.
And the Lord said unto Moses, Pharaoh’s heart is hardened, he refuseth to let the people go.
Get thee unto Pharaoh in the morning; lo, he goeth out unto the water; and thou shalt stand by the river’s brink against he come; and the rod which was turned to a serpent shalt thou take in thine hand.
Counter-Arguments
The strongest case that this verse does not belong in this theme.

Cross-References
“And the Lord said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.”
“And the Lord said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.”
“Wherefore then do ye harden your hearts, as the Egyptians and Pharaoh hardened their hearts? when he had wrought wonderfully among them, did they not let the people go, and they departed?”
“He hath blinded their eyes, and hardened their heart; that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them.”
“And I will harden Pharaoh’s heart, and multiply my signs and my wonders in the land of Egypt.”