Exodus 4:21
“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 in Midian, Go, return into Egypt: for all the men are dead which sought thy life.
And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand.
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 thou shalt say unto Pharaoh, Thus saith the Lord, Israel is my son, even my firstborn:
And I say unto thee, Let my son go, that he may serve me: and if thou refuse to let him go, behold, I will slay thy son, even thy firstborn.
Counter-Arguments
The strongest case that this verse does not belong in this theme.

Related Verses
“And Moses and Aaron did all these wonders before Pharaoh: and the Lord hardened Pharaoh’s heart, so that he would not let the children of Israel go out of his land.”
“And the Lord said unto Moses, Pharaoh’s heart is hardened, he refuseth to let the people go.”
“And the Lord said unto Moses, Go in unto Pharaoh: for I have hardened his heart, and the heart of his servants, that I might shew these my signs before him:”
“And I will harden Pharaoh’s heart, and multiply my signs and my wonders in the land of Egypt.”
“But the Lord hardened Pharaoh’s heart, so that he would not let the children of Israel go.”