Musnad Abu Ya'la al-Mawsili 159:135

Shayban narrated to us, Ammarah ibn Zadhan al-Saydalani narrated to us, Ali ibn al-Hakam narrated to us, from Ata ibn Abi Rabah, from Abu Hurayrah, from the Prophet, may Allah bless him and grant him peace, who said: "There is no man who memorizes knowledge, then is asked about it and conceals it, except that he will be brought on the Day of Resurrection bridled with a bridle of fire."