Hebrews 3:8

do not harden your hearts as your forefathers did in the time of the provocation on the day of the temptation in the Desert,

Hebrews 3:15

seeing that the warning still comes to us, "To-day, if you hear His voice, do not harden your hearts as your forefathers did in the time of the provocation."

Revelation 16:9

And the men were severely burned; and yet they spoke evil of God who had power over the plagues, and they did not repent so as 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
do not harden your hearts as your forefathers did in the time of the provocation on the day of the temptation in the Desert,
Revelation 16:9
And the men were severely burned; and yet they spoke evil of God who had power over the plagues, and they did not repent so as to give Him glory.