Sahih Bukhari Volume 9, Book 92, Hadith Number 410.

Narrated By ‘Abdullah bin ‘Amr : I heard the Prophet saying, “Allah will not deprive you of knowledge after he has given it to you, but it will be taken away through the death of the religious learned men with their knowledge. Then there will remain ignorant people who, when consulted, will give verdicts according to their opinions whereby they will mislead others and go astray.”