The occasion of the revelation of Surah al-Anfal

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that on the day of Badr the Messenger of Allah (peace and blessings be upon him) said: "Whoever does such-and-such (an act of bravery) will receive such-and-such a reward (nafl) from the spoils." The narrator says: (Hearing this) the young men went forward, while the elders considered it necessary to stay by the banners and did not move from there. Then when Allah granted them victory, the elders said: "We were your support; had you been defeated, you would have fallen back to us. So do not take away all the spoils while we are left empty-handed." The young men refused and said: "The Messenger of Allah (peace and blessings be upon him) has fixed this reward for us." Then Allah Almighty revealed this verse: "They ask you about the spoils of war. Say: The spoils of war belong to Allah and the Messenger," up to where He said: "Just as your Lord brought you out of your home with the truth, while a party of the believers were averse to it" [Al-Anfal: 1-5]. That is, that (distribution) proved to be better for them. So in the same way, obey me (in decisions), for I know the outcome of these matters better than you.
This hadith is sahih (authentic), for Imam Bukhari used Ikrimah as evidence and Imam Muslim used Dawud bin Abi Hind as evidence, but they did not record it.

It is narrated from Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him): On the day of Badr I came to the Prophet (peace and blessings be upon him) with a sword and said: O Messenger of Allah, today my heart has been soothed (by fighting) against the enemy, so grant me this sword. He (peace and blessings be upon him) said: "This sword is neither mine nor yours (rather, it belongs to Allah)." I went away saying: Today it will be given to someone who has not endured what I have endured. Meanwhile a messenger came to me and said: Respond (to the call of the Prophet (peace and blessings be upon him)). I thought that perhaps some revelation had come down about what I had said. I came, and the Prophet (peace and blessings be upon him) said: "You asked me for this sword while it was neither mine nor yours; now Allah has given it to me, so (now) it is yours." Then he (peace and blessings be upon him) recited this verse: "They ask you about the spoils of war. Say: The spoils of war belong to Allah and the Messenger."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.