Musnad Ahmad 528:9

Yazid ibn Abd Rabbih narrated to us, he said: Al-Walid ibn Muslim narrated to us, from Muhammad ibn Muhajir, from Al-Walid ibn Abd al-Rahman al-Jurashi, from Jubayr ibn Nufayr, he said: I heard Al-Nawwas ibn Sam'an al-Kilabi saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The Quran will be brought on the Day of Resurrection, and its people who used to act upon it, preceded by Surah Al-Baqarah and Ali 'Imran." And the Messenger of Allah, peace and blessings of Allah be upon him, struck three similitudes for them, which I have not forgotten since: "As if they were two clouds, or two black canopies, between them there is light, or as if they were two flocks of birds in formation, pleading for their companion."