Mark 6:52
for they had not understood about the loaves, because their hearts were hardened.
Mark 3:5
And he looked around at them with anger, grieved at the hardness of their hearts, and said to the man, "Stretch out your hand." He stretched it out, and his hand was restored.
Mark 8:17-21
Being aware of it, Jesus said to them, "Why do you discuss the fact that you have no bread? Do you not yet perceive or understand? Are your hearts hardened?
Matthew 16:9-11
Do you not yet perceive? Do you not remember the five loaves of the five thousand, and how many baskets you gathered?
Mark 7:18
So he said to them, "Are you also without understanding? Do you not see that whatever enters a man from outside cannot defile him,
Mark 16:14
Later he appeared to the eleven as they sat at the table; and he rebuked them for their unbelief and hardness of heart, because they did not believe those who had seen him after he had risen.
Luke 24:25
And he said to them, "O foolish men, and slow of heart to believe all that the prophets have spoken!
Romans 11:7
What then? Israel did not obtain what it sought. The elect obtained it, but the rest were hardened,