Mbh 12.142.2b

Those who seek to acquire knowledge for the object only of carrying their sustenance by it, O king, are sinful besides being enemies of morality. Wicked men, of immature understandings, can never know things truly, even as persons unconversant with scriptures are unable in all their acts to be guided by reason. With eyes directed to the faults of the scriptures, they decry the scriptures. Even if they understand the true meaning of the scriptures, they are still in the habit of proclaiming that scriptural injunctions are unsound. Such men, by decrying the knowledge of others proclaim the superiority of their own knowledge. They have words for their weapons and words for their arrows and speak as if they are real masters of their sciences. Know, O Bharata, that they are traders in learning and Rakshasas among men. By the aid of mere pretexts they cast off that morality which has been established by good and wise men. It has been heard by us that the texts of morality are not to be understood by either discussion or one's own intelligence. Indra himself has said that this is the opinion of the sage Vrihaspati. Some are of opinion that no scriptural text has been laid down without a reason. Others again, even if they properly understand the scriptures, never act according to them. One class of wise men declare that morality is nothing else than the approved course of the world. The man of true knowledge should find out for himself the morality laid down for the good. If even a wise man speaks of morality under the influence of wrath or confusion of understanding or ignorance, his deliverances go for nothing. Discourses on morality made with the aid of an intelligence that is derived from the true letter and spirit of the scriptures, are worthy of praise and not those which are made with the help of anything else. Even the words heard from an ignorant person, if in themselves they be fraught with sense, come to be regarded as pious and wise.