Musnad Abu Ya'la al-Mawsili 155:340

'Abd al-Rahman ibn Salih al-Azdi narrated to us, 'Abd al-Rahim narrated to us, Yazid ibn Kisan narrated to us, from Abu Hazim, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Gather, for I will recite to you a third of the Qur'an." So they gathered, and he recited to us: "Say, 'He is Allah, [who is] One,'" until he concluded it. Then he entered [his house]. Some of us said: "The Prophet (may Allah bless him and grant him peace) had said, 'I will recite to you a third of the Qur'an,' and he did not recite [anything else]. This is only because of news that came to him from the heaven." He said: Then he came out to us and said: "Indeed, it is a third of the Qur'an."