Sahih Bukhari Volume 9, Book 88, Hadith Number 187.

Narrated By ‘Abdullah : The Prophet said, “Near the establishment of the Hour, there will be the days of Al-Harj, and the religious knowledge will be taken away (vanish i.e. by the death of Religious scholars) and general ignorance will spread.” Abu Musa said, “Al-Harj, in the Ethiopian language, means killing,” Ibn Mas’ud added: I heard Allah’s Apostle saying; (It will be) from among the most wicked people who will be living at the time when the Hour will be established.”