From Sahih Bukhari (Hadith 100):
Narrated `Abdullah bin `Amr bin Al-`As:I heard Allah's Messenger (ﷺ) 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 people astray
Reference: Bukhari 100