Exodus 8:15

But when Pharaoh saw that there had come a respite, then made he his heart dull and hearkened not unto them, - as spake Yahweh.

Exodus 7:4

And Pharaoh will not hearken unto you, so will I lay my hand on Egypt, - and bring forth my hosts - my people the sons of Israel out of the land of Egypt, with great judgments.

Ecclesiastes 8:11

Because sentence against a wicked work is not executed speedily - on this account, the heart of the sons of men is fully set within them, to commit wickedness.

Exodus 4:21

And Yahweh said unto Moses, When thou goest to return to Egypt, see as touching all the wonders which I have put in thy hand, that thou do them before Pharaoh - but, I, will let his heart wax bold, and he will not suffer the people to go.

Exodus 7:13-14

Then waxed bold the heart of Pharaoh, and he hearkened not unto them, - as spake Yahweh.

Exodus 14:5

And it was told the king of Egypt, that the people had fled, - and the heart of Pharaoh and his servants was turned against the people, and they said - What is this we have done, that we have let Israel go from serving us?

Proverbs 29:1

He that being often reproved stiffeneth his neck, suddenly shall be hurt, and there be no healing.

Isaiah 26:10

Let favour be shewed to the lawless, he hath not learned righteousness, In a land of honest dealings, he acteth perversely, - And seeth not the splendour of Yahweh.

Jeremiah 34:7-11

when, the force of the king of Babylon, was fighting against Jerusalem, and against all the cities of Judah that were left, - against Lachish and against Azekah, for they, remained among the cities of Judah as fortified cities.

Hosea 6:4

What can I do unto thee, O Ephraim? What can I do unto thee, O Judah? for, your lovingkindness, is like a morning cloud, yea, like the dew, early departing!

Zechariah 7:11-12

Howbeit they refused to give heed, but put forth a rebellious shoulder, - and, their ears, made they hard of hearing, that they might not hear;

Hebrews 3:8

harden your hearts, - as in the embitterment, in the day of testing in the desert,

Hebrews 3:15

So long as it is said - To-day, if, unto his voice, ye would hearken, do not harden your hearts, - as in the embitterment.

Revelation 16:9

and mankind were scorched with a great scorching heat, and they blasphemed the name of God who had authority over these plagues, and repented not to give him glory.

Treasury of Scripture Knowledge

Summary

But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the LORD had said.

Bible References

He hardened

Exodus 4:21
And Yahweh said unto Moses, When thou goest to return to Egypt, see as touching all the wonders which I have put in thy hand, that thou do them before Pharaoh - but, I, will let his heart wax bold, and he will not suffer the people to go.
Exodus 7:4
And Pharaoh will not hearken unto you, so will I lay my hand on Egypt, - and bring forth my hosts - my people the sons of Israel out of the land of Egypt, with great judgments.
Proverbs 29:1
He that being often reproved stiffeneth his neck, suddenly shall be hurt, and there be no healing.
Zechariah 7:11
Howbeit they refused to give heed, but put forth a rebellious shoulder, - and, their ears, made they hard of hearing, that they might not hear;
Hebrews 3:8
harden your hearts, - as in the embitterment, in the day of testing in the desert,
Revelation 16:9
and mankind were scorched with a great scorching heat, and they blasphemed the name of God who had authority over these plagues, and repented not to give him glory.

General references

Exodus 7:13
Then waxed bold the heart of Pharaoh, and he hearkened not unto them, - as spake Yahweh.
Exodus 8:32
And Pharaoh made his heart dull, this time also, - and did not let the people go.
Jeremiah 34:11
howbeit they turned after that, and brought back the servants and the handmaids whom they had let go, free, and brought them into subjection as servants and as handmaids,