Mark 16:14:

Afterward he appeared unto the eleven as they sat at meat, and upbraided them with their unbelief and hardness of heart, because they believed not them which had seen him after he was risen.

See also:

If God Gives Everyone Faith, How Can Anyone Ever Be in Unbelief? Isn’t Unbelief the Absence of Faith?
Does Faith Come from Your Spirit, Your Mind or Somewhere Else?
What Is the Difference Between Unbelief and Doubt?