The Messenger of Allah ﷺ said, "When your brothers were struck down at Uhud, Allah placed their souls inside green birds that drink from the rivers of Paradise, eat from its fruits, and take shelter in lamps of gold suspended in the shade of the Throne. When they tasted the goodness of their food, drink, and resting place, they said, 'Who will convey to our brothers on our behalf that we are alive in Paradise and provided for, so that they will not lose interest in jihad nor shrink back from war?' Allah, glorified be He, said, 'I will convey it to them on your behalf.'"He said, then Allah revealed "And do not think of those who have been killed in the way of Allah..." [Aal Imran 3:169] to the end of the verse.
قال رسول الله ﷺ: لما أصيب إخوانكم بأحد جعل الله أرواحهم في جوف طير خضر ترد أنهار الجنة تأكل من ثمارها وتأوي إلى قناديل من ذهب معلقة في ظل العرش فلما وجدوا طيب مأكلهم ومشربهم ومقيلهم قالوا: من يبلغ إخواننا عنا أنا أحياء في الجنة نرزق لئلا يزهدوا في الجهاد ولا ينكلوا عند الحرب فقال الله سبحانه: أنا أبلغهم عنكم قال: فأنزل الله {ولا تحسبن الذين قتلوا في سبيل الله} إلى آخر الآية.
Abu Dawud (2520) narrated it from Uthman bin Abu Shayba, who said, Abdullah bin Idris told us, from Muhammad bin Ishaq, from Ismail bin Umaya, from Abu Zubayr, from Saeed bin Jubayr, from Ibn Abbas, who said, and then he mentioned it. It is a hasan hadith. See the detailed discussion of this in the Book of Faith, the hadiths concerning the Throne.