Musnad Ahmad 1017:115

Waki’ narrated to us, Bashir ibn al-Muhajir narrated to us, from ‘Abdullah ibn Buraydah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Learn Al-Baqarah and Al-'Imran, for they are the two radiant ones. They will come on the Day of Resurrection as if they are two clouds, or as if they are two shades, or as if they are two flocks of birds in rows, pleading for their companion." And Waki’ said once: "Arguing for their companion."