Musnad Ahmad 25:530

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Isma'il bin Umayyah bin 'Amr bin Sa'id narrated to me, from Abu al-Zubayr al-Makki, from Ibn 'Abbas, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "When your brothers were struck at Uhud, Allah, the Almighty and Majestic, placed their souls in the bellies of green birds that frequent the rivers of Paradise, eat from its fruits, and nest in lanterns of gold in the shade of the Throne. When they found the goodness of their drink, their food, and their beautiful resting place, they said: 'Would that our brothers knew what Allah has done for us, so that they would not turn away from Jihad and would not refrain from war.' So Allah, the Almighty and Majestic, said: 'I will inform them of you.'" Then Allah, the Almighty and Majestic, revealed these verses to His Messenger: {And do not think of those who have been killed in the way of Allah as dead...} [Al 'Imran: 169].