'Unbelief' in the Bible

He marveled because of their unbelief. He went around the villages teaching.

Immediately the father of the child cried out with tears, "I believe. Help my unbelief!"

Afterward he was revealed to the eleven themselves as they sat at the table, and he rebuked them for their unbelief and hardness of heart, because they didn't believe those who had seen him after he had risen.