Mark 6:52
for they had not understood about the loaves; on the contrary their heart was hardened.
Mark 3:5
They were silent. Then looking around upon them with anger, and deeply grieved by the hardening of their hearts, he said to the man, "Stretch out your hand!" He stretched it out, and the hand was at once completely restored.
Mark 8:17-21
"Why are you arguing together because you have no bread? Do you not yet perceive and understand?
Matthew 16:9-11
"Do you not remember the five loaves for the five thousand, and how many large basketfuls you took up?
Mark 7:18
"Are even you without understanding?" he said. "Do you not perceive that nothing whatever from without can defile a man by entering him,
Mark 16:14
Afterward he appeared to the Eleven themselves, as they were eating, and reproached them for their lack of faith, and stubborn hearts, because they disbelieved those who had seen him risen.
Luke 24:25
"O foolish men," said Jesus, "slow of heart to believe all that the prophets have spoken!
Romans 11:7
What then? that which Israel has been seeking for, that he has not obtained; but the chosen have obtained it, and the rest have been hardened.