Hasan al-Basree 110 AH (may Allah have mercy on him) said:

العلم علمان: علم في القلب, و علم على اللسان, فعلم القلب هو العلم النافع, و علم اللسان هو حجة الله على عباده

“Knowledge is two (types): Knowledge in the heart and knowledge upon the tongue. Knowledge of the heart is the beneficial knowledge, and knowledge on the tongue is a proof of Allah upon His slave.”

“It is a proof of Allah upon His slave” Meaning: if the slave acts upon what he says then his statement will be a proof for him, but if he doesn’t act upon it then it will be a proof against him.

Collected by Shaykhul Islaam ibn Taymeeyah in his fataawa 7:23