Musnad Abu Ya'la al-Mawsili 110:259

Zuhayr narrated to us, Yunus ibn Muhammad narrated to us, Abu 'Awanah narrated to us, from 'Abd al-A'la, from Sa'id ibn Jubayr, from Ibn 'Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever is asked about knowledge and conceals it, he will come on the Day of Resurrection bridled with a bridle of fire. And whoever speaks about the Qur'an without what he knows, he will come on the Day of Resurrection bridled with a bridle of fire."