Musnad Ahmad 937:84

Mu'ammal narrated to us, Hammad narrated to us, Hajjaj al-Aswad narrated to us—Mu'ammal said: "And he was a righteous man"—he said: I heard Abu al-Siddiq narrating to Thabit al-Bunani, from a man, from Abu Dharr, that the Prophet, peace and blessings of Allah be upon him, said: "You are in a time whose scholars are many and whose speakers are few. Whoever abandons a tenth of what he knows in it will follow his desires," or he said: "will perish." "And a time will come upon the people when its scholars will be few and its speakers will be many. Whoever holds fast in it to a tenth of what he knows will be saved."