Narrated `Aisha:The day of Bu'ath was a day (i.e. battle) which Allah caused to take place just before the mission of His Apostle so that when Allah's Messenger (ﷺ) came to Medina, they (the tribes) had divided (into hostile groups) and their nobles had been killed; and all that facilitated their conversion to Islam.
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ قَالَتْ كَانَ يَوْمُ بُعَاثٍ يَوْمًا قَدَّمَهُ اللَّهُ عَزَّ وَجَلَّ لِرَسُولِهِ صلى الله عليه وسلم، فَقَدِمَ رَسُولُ اللَّهِ صلى الله عليه وسلم الْمَدِينَةَ وَقَدِ افْتَرَقَ مَلَؤُهُمْ، وَقُتِلَتْ سَرَاتُهُمْ فِي دُخُولِهِمْ فِي الإِسْلاَمِ.
Bukhari
Merits of the Helpers in Madinah (Ansaar) • Hadith 155