Imām Aḥmad رحمه الله said:

“DO NOT write from three:

• A PERSON OF INNOVATION* who calls to his Bidʿah.

• Or a LIAR for indeed nothing is written from him; be it less or a lot.

• Or from a man who makes a mistake but DOES NOT RECTIFY it when he is refuted.”

[الكافية ١٤٤]