Musnad Ahmad 28:419

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, from 'Urwah, from 'Abdullah ibn 'Amr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah does not snatch away knowledge from the people after He has given it to them, but He takes away the scholars. Whenever a scholar departs, he takes with him the knowledge that he possesses, until there remains only those who do not know. Then the people will take ignorant leaders, and they will be asked for religious verdicts, so they will give verdicts without knowledge; thus, they will go astray and lead others astray."