A Companion diagnosed himself, and was wrong

Hanzala, may Allah be pleased with him, went to Abu Bakr and said Hanzala has become a hypocrite.

His reason was this. When he was with the Prophet, peace be upon him, his state was one thing. When he went home to his wife and his children and his work, it was another. He took the fluctuation as evidence of nifaq in himself.

Abu Bakr said the same happened to him. They took it to the Prophet, peace be upon him, and the charge was not accepted.

That is the exact error this course exists to correct, made by a Companion, about himself, in front of the Prophet, and answered.