It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him), (the narrator said: most likely this is a marfu' report,) that the Messenger of Allah (peace and blessings be upon him) said: "Before the Hour there will be days of harj (killing and turmoil), in which knowledge will be taken away and ignorance will descend."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10433