'Unbelief' in the Bible

And he marvelled because of their unbelief. And he went round about the villages teaching.

Straightway the father of the child cried out, and said, I believe; help thou mine unbelief.

And afterward he was manifested unto the eleven themselves as they sat at meat; and he upbraided them with their unbelief and hardness of heart, because they believed not them that had seen him after he was risen.