Sahih Muslim 6413
صحيح مسلم#6413SahihJabir b. Abdullah reported that it was concerning them (the Ansar) that this verse was revealed, that when the two groups amongst you were about to lose heart and Allah was the Guardian of them both. This concerned Banu Salama and Banu Haritha and we did not like that Allah, the Exalted and Glorious, should not have revealed this verse for the fact that Allah (gave an assurance) of being the Guardian of both
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 44:243