Luke 24:25
And He said to them, "O inconsiderate and slow in heart to believe in all that the prophets spake!
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 8:17-18
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?
Mark 9:19
And He, answering, saith to them, "O faithless generation! how long shall I be with you! how long shall I bear with you? Bring him to Me."
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.
Hebrews 5:11-12
Concerning Whom we have much to say and difficult to explain, since ye have become dull of hearing.