Sahih Bukhari | Volume 5 | Hadith Number 267

Narrated 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.