Hebrews 3:8
harden not your hearts, as in the provocation, in the day of the temptation in the wilderness,
Matthew 13:15
For this peoples heart hath become gross, and their ears are dull of hearing, and their eyes they have closed, lest they should see with their eyes, and hear with their ears, and understand with their heart, and turn from their ways, and I should heal them."
Acts 19:9
But when some were hardened, and believed not, but spoke evil of the way [of the Lord] before the multitude, he departed from them, and separated the disciples, discoursing daily in the school of Tyrannus.
Romans 2:5-6
But according to thy hardness and impenitent heart, thou art treasuring up for thyself wrath against the day of wrath and of the manifestation of the righteous judgment of God,
1 Corinthians 10:9
Nor let us tempt Christ, as some of them tempted, and were destroyed by the serpents.
Hebrews 3:12-13
Take heed, brethren, lest there be in any one of you an evil heart of unbelief, in departing from the living God.