Sahih Bukhari Volume 5, Book 58, Hadith Number 267.

Narated By ‘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 Apostle 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.