Mark 6:52
for they did not understand concerning the loaves, but their heart was hardened.
Mark 3:5
And having looked round about on them with anger, and being grieved at the hardness of their heart, He saith to the man, "Stretch forth your hand." And he stretched it forth; and his hand was restored.
Mark 8:17-21
And perceiving it, He saith to them, "Why are ye reasoning because ye have no bread? Do ye not yet perceive, nor understand? Have ye your heart hardened?
Matthew 16:9-11
Do ye not yet perceive, nor remember the five loaves of the five thousand, and how many baskets ye took up?
Mark 7:18
And He saith to them, "Are ye too thus without understanding? Do ye not perceive that nothing, entering into a man from without, can defile him;
Mark 16:14
And afterward He was manifested to the eleven themselves, as they were reclining at table, and upbraided them for their unbelief and hardness of heart, because they believed not those who saw Him after He had risen.
Luke 24:25
And He said to them, "O inconsiderate and slow in heart to believe in all that the prophets spake!
Romans 11:7
What, then? What Israel is seeking for, this he did not obtain; but the election obtained it, and the rest were hardened;