Musnad Ahmad 28:35

Yahya narrated to me, from Hisham, who dictated it to us: My father narrated to me, I heard Abdullah ibn Amr, from his mouth to my mouth, saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, Allah does not take away knowledge by snatching it away from the people, but He takes away knowledge by the death of the scholars, until when He leaves no scholar, the people take ignorant leaders. They are asked, so they give fatwas without knowledge, and thus they go astray and lead others astray."