He who practices Tasawwuf without learning Sacred Law corrupts his faith, while he who learns Sacred Law without practicing Tasawwuf corrupts himself. 

Only he who combines the two proves true.

Malik ibn Anas

Only that which was effective for the first of this community will be effective for the last of it

Malik ibn Anas

Knowledge is not to be taken from four types of people: a foolish person who openly acts foolish, even if he reports the most narrations; an adherent of bid'ah who calls to his desires; a person who lies, even if I don't accuse him of lying in hadith; and a righteous pious worshiper who does not accurately retain what he narrates.

Malik ibn Anas