Musnad Ahmad 30:1517

Hassan narrated to us, Hammad ibn Salamah narrated to us, from Ali ibn al-Hakam, from Ata ibn Abi Rabah, from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever is asked about knowledge and conceals it, Allah will bridle him with a bridle of fire."