This Bible contradiction is from the Skeptic's Annotated Bible.
Exodus 4:21 View context
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.
Exodus 7:3-13 View context
And I will harden Pharaoh's heart, and multiply my signs and my wonders in the land of Egypt.
But Pharaoh shall not hearken unto you, that I may lay my hand upon Egypt, and bring forth mine armies, [and] my people the children of Israel, out of the land of Egypt by great judgments.
And the Egyptians shall know that I [am] the LORD, when I stretch forth mine hand upon Egypt, and bring out the children of Israel from among them.
And Moses and Aaron did as the LORD commanded them, so did they.
And Moses [was] fourscore years old, and Aaron fourscore and three years old, when they spake unto Pharaoh.
And the LORD spake unto Moses and unto Aaron, saying,
When Pharaoh shall speak unto you, saying, Shew a miracle for you: then thou shalt say unto Aaron, Take thy rod, and cast [it] before Pharaoh, [and] it shall become a serpent.
And Moses and Aaron went in unto Pharaoh, and they did so as the LORD had commanded: and Aaron cast down his rod before Pharaoh, and before his servants, and it became a serpent.
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.
Exodus 9:12 View context
And the LORD hardened the heart of Pharaoh, and he hearkened not unto them; as the LORD had spoken unto Moses.
Exodus 10:1-27 View context
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 that thou mayest tell in the ears of thy son, and of thy son's son, what things I have wrought in Egypt, and my signs which I have done among them; that ye may know how that I [am] the LORD.
And Moses and Aaron came in unto Pharaoh, and said unto him, Thus saith the LORD God of the Hebrews, How long wilt thou refuse to humble thyself before me? let my people go, that they may serve me.
Else, if thou refuse to let my people go, behold, to morrow will I bring the locusts into thy coast:
And they shall cover the face of the earth, that one cannot be able to see the earth: and they shall eat the residue of that which is escaped, which remaineth unto you from the hail, and shall eat every tree which groweth for you out of the field:
And they shall fill thy houses, and the houses of all thy servants, and the houses of all the Egyptians; which neither thy fathers, nor thy fathers' fathers have seen, since the day that they were upon the earth unto this day. And he turned himself, and went out from Pharaoh.
And Pharaoh's servants said unto him, How long shall this man be a snare unto us? let the men go, that they may serve the LORD their God: knowest thou not yet that Egypt is destroyed?
And Moses and Aaron were brought again unto Pharaoh: and he said unto them, Go, serve the LORD your God: [but] who [are] they that shall go?
And Moses said, We will go with our young and with our old, with our sons and with our daughters, with our flocks and with our herds will we go; for we [must hold] a feast unto the LORD.
And he said unto them, Let the LORD be so with you, as I will let you go, and your little ones: look [to it]; for evil [is] before you.
Not so: go now ye [that are] men, and serve the LORD; for that ye did desire. And they were driven out from Pharaoh's presence.
And the LORD said unto Moses, Stretch out thine hand over the land of Egypt for the locusts, that they may come up upon the land of Egypt, and eat every herb of the land, [even] all that the hail hath left.
And Moses stretched forth his rod over the land of Egypt, and the LORD brought an east wind upon the land all that day, and all [that] night; [and] when it was morning, the east wind brought the locusts.
And the locusts went up over all the land of Egypt, and rested in all the coasts of Egypt: very grievous [were they]; before them there were no such locusts as they, neither after them shall be such.
For they covered the face of the whole earth, so that the land was darkened; and they did eat every herb of the land, and all the fruit of the trees which the hail had left: and there remained not any green thing in the trees, or in the herbs of the field, through all the land of Egypt.
Then Pharaoh called for Moses and Aaron in haste; and he said, I have sinned against the LORD your God, and against you.
Now therefore forgive, I pray thee, my sin only this once, and intreat the LORD your God, that he may take away from me this death only.
And he went out from Pharaoh, and intreated the LORD.
And the LORD turned a mighty strong west wind, which took away the locusts, and cast them into the Red sea; there remained not one locust in all the coasts of Egypt.
But the LORD hardened Pharaoh's heart, so that he would not let the children of Israel go.
And the LORD said unto Moses, Stretch out thine hand toward heaven, that there may be darkness over the land of Egypt, even darkness [which] may be felt.
And Moses stretched forth his hand toward heaven; and there was a thick darkness in all the land of Egypt three days:
They saw not one another, neither rose any from his place for three days: but all the children of Israel had light in their dwellings.
And Pharaoh called unto Moses, and said, Go ye, serve the LORD; only let your flocks and your herds be stayed: let your little ones also go with you.
And Moses said, Thou must give us also sacrifices and burnt offerings, that we may sacrifice unto the LORD our God.
Our cattle also shall go with us; there shall not an hoof be left behind; for thereof must we take to serve the LORD our God; and we know not with what we must serve the LORD, until we come thither.
But the LORD hardened Pharaoh's heart, and he would not let them go.
Exodus 11:10 View context
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.
Exodus 14:4-17 View context
And I will harden Pharaoh's heart, that he shall follow after them; and I will be honoured upon Pharaoh, and upon all his host; that the Egyptians may know that I [am] the LORD. And they did so.
And it was told the king of Egypt that the people fled: and the heart of Pharaoh and of his servants was turned against the people, and they said, Why have we done this, that we have let Israel go from serving us?
And he made ready his chariot, and took his people with him:
And he took six hundred chosen chariots, and all the chariots of Egypt, and captains over every one of them.
And the LORD hardened the heart of Pharaoh king of Egypt, and he pursued after the children of Israel: and the children of Israel went out with an high hand.
But the Egyptians pursued after them, all the horses [and] chariots of Pharaoh, and his horsemen, and his army, and overtook them encamping by the sea, beside Pi-hahiroth, before Baal-zephon.
And when Pharaoh drew nigh, the children of Israel lifted up their eyes, and, behold, the Egyptians marched after them; and they were sore afraid: and the children of Israel cried out unto the LORD.
And they said unto Moses, Because [there were] no graves in Egypt, hast thou taken us away to die in the wilderness? wherefore hast thou dealt thus with us, to carry us forth out of Egypt?
[Is] not this the word that we did tell thee in Egypt, saying, Let us alone, that we may serve the Egyptians? For [it had been] better for us to serve the Egyptians, than that we should die in the wilderness.
And Moses said unto the people, Fear ye not, stand still, and see the salvation of the LORD, which he will shew to you to day: for the Egyptians whom ye have seen to day, ye shall see them again no more for ever.
The LORD shall fight for you, and ye shall hold your peace.
And the LORD said unto Moses, Wherefore criest thou unto me? speak unto the children of Israel, that they go forward:
But lift thou up thy rod, and stretch out thine hand over the sea, and divide it: and the children of Israel shall go on dry [ground] through the midst of the sea.
And I, behold, I will harden the hearts of the Egyptians, and they shall follow them: and I will get me honour upon Pharaoh, and upon all his host, upon his chariots, and upon his horsemen.
The Pharaoh did.
Exodus 8:15-32 View context
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.
And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast.
Then the magicians said unto Pharaoh, This [is] the finger of God: and Pharaoh's heart was hardened, and he hearkened not unto them; as the LORD had said.
And the LORD said unto Moses, Rise up early in the morning, and stand before Pharaoh; lo, he cometh forth to the water; and say unto him, Thus saith the LORD, Let my people go, that they may serve me.
Else, if thou wilt not let my people go, behold, I will send swarms [of flies] upon thee, and upon thy servants, and upon thy people, and into thy houses: and the houses of the Egyptians shall be full of swarms [of flies], and also the ground whereon they [are].
And I will sever in that day the land of Goshen, in which my people dwell, that no swarms [of flies] shall be there; to the end thou mayest know that I [am] the LORD in the midst of the earth.
And I will put a division between my people and thy people: to morrow shall this sign be.
And the LORD did so; and there came a grievous swarm [of flies] into the house of Pharaoh, and [into] his servants' houses, and into all the land of Egypt: the land was corrupted by reason of the swarm [of flies].
And Pharaoh called for Moses and for Aaron, and said, Go ye, sacrifice to your God in the land.
And Moses said, It is not meet so to do; for we shall sacrifice the abomination of the Egyptians to the LORD our God: lo, shall we sacrifice the abomination of the Egyptians before their eyes, and will they not stone us?
We will go three days' journey into the wilderness, and sacrifice to the LORD our God, as he shall command us.
And Pharaoh said, I will let you go, that ye may sacrifice to the LORD your God in the wilderness; only ye shall not go very far away: intreat for me.
And Moses said, Behold, I go out from thee, and I will intreat the LORD that the swarms [of flies] may depart from Pharaoh, from his servants, and from his people, to morrow: but let not Pharaoh deal deceitfully any more in not letting the people go to sacrifice to the LORD.
And Moses went out from Pharaoh, and intreated the LORD.
And the LORD did according to the word of Moses; and he removed the swarms [of flies] from Pharaoh, from his servants, and from his people; there remained not one.
And Pharaoh hardened his heart at this time also, neither would he let the people go.
Exodus 9:34 View context
And when Pharaoh saw that the rain and the hail and the thunders were ceased, he sinned yet more, and hardened his heart, he and his servants.
1 Samuel 6:6 View context
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?