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."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، قَالَ قَالَ عَمْرٌو سَمِعْتُ جَابِرَ بْنَ عَبْدِ اللَّه ِ ـ رضى الله عنهما ـ يَقُولُ فِينَا نَزَلَتْ {إِذْ هَمَّتْ طَائِفَتَانِ مِنْكُمْ أَنْ تَفْشَلاَ وَاللَّهُ وَلِيُّهُمَا} قَالَ نَحْنُ الطَّائِفَتَانِ بَنُو حَارِثَةَ وَبَنُو سَلِمَةَ، وَمَا نُحِبُّ ـ وَقَالَ سُفْيَانُ مَرَّةً وَمَا يَسُرُّنِي ـ أَنَّهَا لَمْ تُنْزَلْ لِقَوْلِ اللَّهِ {وَاللَّهُ وَلِيُّهُمَا}
sunnah.com