From Sahih Bukhari (Hadith 4558):
Narrated Jabir bin `Abdullah:The Verse:--"When two parties from among you were about to lose heart, but Allah was their Protector," (3.122) was revealed concerning us, and we were the two parties, i.e. Banu Haritha and Banu Salama, and we do not wish (that it had not been revealed) or I would not have been pleased (if it had not been revealed), for Allah says:--"...Allah was their Protector
Reference: Bukhari 4558