Imam Dar ul-Hijrah, Imam Malik ibn Anas {The Mercy of Allah be upon him} said:
“Knowledge is not to be taken from four types of people:
1} A foolish person who openly acts foolish, even if he reports the most narrations;
2} an adherent of bid’ah who calls to his desires;
3} a person who lies, even if I don’t accuse him of lying in regard to Hadith; and
4} a righteous and pious worshiper who does not accurately retain what he narrates.”
{The Lives of the Noble Figures}