Luke 24:25
And he said to them, O ye unwise, and slow in heart to believe in all things which the prophets spake:
Mark 7:18
And he says, So are ye also without understanding? Do ye not perceive, that anything from without entering into a man, cannot pollute him
Mark 8:17-18
And Jesus having known, says to them, Why reason ye with yourselves, because ye have no loaves? observe ye not yet, neither understand? have ye your heart yet hardened?
Mark 9:19
And he having answered, says to him, O faithless generation, how long shall I be with you how long shall I bear with you? bring him to me.
Mark 16:14
Afterwards to those reclining at table was he manifested, and he reproached their unbelief and hard heart, because they believed not them having seen him raised.
Hebrews 5:11-12
Of whom great is the word to us, and difficult of interpretation to speak, since ye have been sluggish in the hearing.