Musnad Ahmad 1018:68

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Abu Ishaq, that he heard Abu Hudhayfah narrating from a man among the companions of the Prophet, may God bless him and grant him peace, from the Prophet, may God bless him and grant him peace, who said: "I looked at the moon on the morning of the Night of Decree (Laylat al-Qadr), and I saw it as if it were a piece of a bowl." And Abu Ishaq said: "The moon is only like that on the morning of the twenty-third night."