Shaykh Ibn ‘Uthaymīn (رحمه الله) stated:
Also, know that from the most important things for the student of knowledge to know are axioms and foundational principles because they are with what knowledge is consolidated.
The Shaykh continues...
In this article taken from Shaykh Ibn ‘Uthaymīn's (رحمه الله) explanation of Riyāḍ al-Ṣāliḥīn, in the ḥadīth of ‘Ā`ishah wherein The Prophet (صلى الله عليه وسلم) said about a man, “What an awful companion he is for those whom he lives amongst,” the Shaykh expounds on the obligation of exposing the condition of one who possesses negative qualities in order to protect others from his harm. This article was translated by our noble brother Abu Afnaan Muhammad 'Abdullah (حفظه الله)
An excerpt taken from the article ~
"Thus, if you see an individual and he is one of debauchery and distrust, yet he has enthralled the people with his eloquence and speech and the people take from him and think he is upon good, it is incumbent upon you to elucidate to them that there is no good in him and speak ill of him so that the people are not deceived by him. How many individuals speak well and are eloquent speakers! If you see them, you are pleased by their physical appearances and if they were to speak, you would listen. Yet, the reality is that there is no good in an individual like this and it is obligatory for you to explain his condition.”