Luke 24:25
Then he said to them, O foolish, and slow of heart to believe all that the prophets have spoken!
Mark 7:18
And he saith to them, Are even ye so without understanding? Do ye not perceive, That whatsoever entereth into a man from without, cannot defile him,
Mark 8:17-18
And Jesus knowing it saith to them, Why reason ye, because ye have no bread? Perceive ye not yet, neither consider? Have ye your heart yet hardened?
Mark 9:19
He answereth them and saith, O faithless generation, how long shall I be with you?
Mark 16:14
Afterwards he appeared to the eleven, sitting at meat, and upbraided them with their unbelief and hardness of heart, because they believed not them who had seen him after he was risen.
Hebrews 5:11-12
Concerning whom we have many things to say, and hard to be explained, seeing ye are become dull of hearing.