Hebrews 3:8

harden not your hearts, as in the provocation, in the day of temptation in the wilderness,

Hebrews 3:15

while it is said, "To-day, if ye hear His voice, harden not your hearts as in the provocation."

Revelation 16:9

And the men were scorched with great heat; and they blasphemed the name of God, Who hath the power over these plagues; and they 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

Hebrews 3:8
harden not your hearts, as in the provocation, in the day of temptation in the wilderness,
Revelation 16:9
And the men were scorched with great heat; and they blasphemed the name of God, Who hath the power over these plagues; and they repented not, to give Him glory.