Luke 24:25
Then Jesus said to them: "O foolish men, slow to accept all that the Prophets have said!
Mark 7:18
"What, do even you understand so little?" exclaimed Jesus. "Do not you see that there is nothing external to a man, which by going into a man, can 'defile' him,
Mark 8:17-18
And, noticing this, Jesus said to them: "Why are you talking about your being short of bread? Do not you yet see or understand? Are your minds still so slow or comprehension?
Mark 9:19
"O faithless generation!" exclaimed Jesus. "How long must I be with you? how long must I have patience with you? Bring the boy to me."
Mark 16:14
Later on, he made himself known to the Eleven themselves as they were at a meal, and reproached them with their want of faith and their stubbornness, because they did not believe those who had seen him after he had risen from the dead.
Hebrews 5:11-12
Now on this subject I have much to say, but it is difficult to explain it to you, because you have shown yourselves so slow to learn.