Hebrews 3:8

harden not your hearts, as in that bitter provocation, at the day of the temptation in the wilderness;

Hebrews 3:15

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

Revelation 16:9

And the men were scorched with a fierce heat, and they blasphemed the name of God, who had 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 that bitter provocation, at the day of the temptation in the wilderness;
Revelation 16:9
And the men were scorched with a fierce heat, and they blasphemed the name of God, who had power over these plagues: and they repented not, to give him glory.