Musnad Ahmad 5:231

Abdullah narrated to us, Muhammad ibn Sulayman Lawin narrated to me, Hudayj narrated to us, from Abu Ishaq, from Abu Hudhayfah, from Ali, who said: The Prophet (peace and blessings of Allah be upon him) said: "I went out when the moon had risen, as if it were a piece of a large bowl." Then he said: "Tonight is the Night of Decree (Laylat al-Qadr)."