"...This is the practice of those dim-witted men who know the truth by men, and not men by the truth. The intelligent man, on the contrary, follows the advice of the Master of the Intelligent, 'Ali - God be pleased with him! - where he says: "Do not know the truth by men, but rather, know the truth and you will know its adherents." The intelligent man, therefore, first knows the truth, then he considers what is actually said by someone. If it is true, he accepts it, whether the speaker be wrong or right in other matters. Indeed, such a man will often be intent on extracting what is true from the involved utterances of the erring, since he is aware that gold is usually found mixed with dirt."
-Imam al-Ghazali in Deliverance from Error, translated by R.J. McCarthy, pg. 68