Exodus 8:15
“But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the Lord had said.”
And the Lord did according to the word of Moses; and the frogs died out of the houses, out of the villages, and out of the fields.
And they gathered them together upon heaps: and the land stank.
But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the Lord had said.
And the Lord said unto Moses, Say unto Aaron, Stretch out thy rod, and smite the dust of the land, that it may become lice throughout all the land of Egypt.
And they did so; for Aaron stretched out his hand with his rod, and smote the dust of the earth, and it became lice in man, and in beast; all the dust of the land became lice throughout all the land of Egypt.
Counter-Arguments
The strongest case that this verse does not belong in this theme.

Cross-References
“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?”
“And Pharaoh hardened his heart at this time also, neither would he let the people go.”
“As a dog returneth to his vomit, so a fool returneth to his folly.”
“Because sentence against an evil work is not executed speedily, therefore the heart of the sons of men is fully set in them to do evil.”
“Let favour be shewed to the wicked, yet will he not learn righteousness: in the land of uprightness will he deal unjustly, and will not behold the majesty of the Lord.”