(And call not those who are slain in the way of Allah “dead”…) [2:154].
This was revealed about those Muslims who were killed at Badr. They were fourteen in total: eight from the Helpers and six from the Migrants. This is because people used to say about any man who was killed for the sake of Allah: “So-and-so has died and will miss all the comfort and pleasures of this worldly life”. And as a response, Allah, exalted is He, revealed this verse.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou