Musnad Ahmad 30:1413

'Affan narrated to us, Hammad ibn Salamah narrated to us, from 'Ali ibn al-Hakam, from 'Ata' ibn Abi Rabah, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever is asked about knowledge and conceals it, Allah the Almighty and Majestic will bridle him with a bridle of fire on the Day of Resurrection."