From Sahih Bukhari (Hadith 4026):
Narrated Ibn Shihab:These were the battles of Allah's Messenger (ﷺ) (which he fought), and while mentioning (the Badr battle) he said, "While the corpses of the pagans were being thrown into the well, Allah's Messenger (ﷺ) said (to them), 'Have you found what your Lord promised true?" `Abdullah said, "Some of the Prophet's companions said, "O Allah's Messenger (ﷺ)! You are addressing dead people.' Allah's Messenger (ﷺ) replied, 'You do not hear what I am saying, better than they.' The total number of Muslim fighters from Quraish who fought in the battle of Badr and were given their share of the booty, were 81 men." Az-Zubair said, "When their shares were distributed, their number was 101 men. But Allah knows it better
Reference: Bukhari 4026