Narrated 'Abdullah bin 'Amr bin Al' As:
I heard Allah's Apostle saying, "Allah does not take away the
knowledge, by taking it away from (the hearts of) the people, but
takes it away by the death of the religious learned men till when
none of the (religious learned men) remains, people will take as
their leaders ignorant persons who when consulted will give their
verdict without knowledge. So they will go astray and will lead the
(Sahih al-Bukhari, Book of al-`Ilm: 3, Hadith No. 100).