Mark 4:40

And He said to His disciples, "Why are you so afraid? Do you not still have [any] faith?"

Matthew 14:31

And immediately Jesus stretched out His hand and took hold of him and said, "You have such little faith; why did you doubt?"

Luke 8:25

Then He said to the disciples, "Where is your faith?" They became afraid and were amazed, saying to one another, "Who can this [man] be, that he can even command the winds and the water and they obey him?"

Matthew 6:30

So, if God so [beautifully] dresses the grass in a field, which is [green] today, and [then] tomorrow [dries up and] is thrown in the oven [i.e., as fuel], will He not do even more in providing your clothing, you people with such little faith?

Matthew 8:26

And He called to them, "Why are you [so] afraid? You have such little faith!" Then He stood up and sternly commanded the wind and the waves, and they became very calm.

Matthew 16:8

Jesus, being aware of their thoughts, said, "O, you people with [such] little faith! Why are you reasoning among yourselves about not having bread?

John 6:19-20

And when the disciples had rowed about three or four miles, they saw Jesus walking on the [surface of the] water. They became afraid as Jesus got closer to their boat.

Treasury of Scripture Knowledge

Summary

And he said unto them, Why are ye so fearful? how is it that ye have no faith?

General references

Bible References

Why

Matthew 8:26
And He called to them, "Why are you [so] afraid? You have such little faith!" Then He stood up and sternly commanded the wind and the waves, and they became very calm.
Matthew 14:31
And immediately Jesus stretched out His hand and took hold of him and said, "You have such little faith; why did you doubt?"
Luke 8:25
Then He said to the disciples, "Where is your faith?" They became afraid and were amazed, saying to one another, "Who can this [man] be, that he can even command the winds and the water and they obey him?"
John 6:19
And when the disciples had rowed about three or four miles, they saw Jesus walking on the [surface of the] water. They became afraid as Jesus got closer to their boat.

No faith

Matthew 6:30
So, if God so [beautifully] dresses the grass in a field, which is [green] today, and [then] tomorrow [dries up and] is thrown in the oven [i.e., as fuel], will He not do even more in providing your clothing, you people with such little faith?
Matthew 16:8
Jesus, being aware of their thoughts, said, "O, you people with [such] little faith! Why are you reasoning among yourselves about not having bread?

General references

Matthew 16:11
How is it that you do not understand that I was not speaking to you about [physical] bread? But [rather I meant] watch out for the yeast [i.e., the influence] of the Pharisees and Sadducees."