Musnad Ahmad 1153:311

Abu Usamah narrated to us, he said: Hisham informed us, from his father, from Aisha, who said: "The day of Bu'ath was a day that Allah, the Mighty and Majestic, had prepared for His Messenger, may Allah bless him and grant him peace. So the Messenger of Allah, may Allah bless him and grant him peace, arrived in Medina while their assembly had been divided, their leaders had been killed, and they had become gentle for the sake of Allah, the Mighty and Majestic, and His Messenger, by entering into Islam."