The day of Bu'ath (i.e. Day of fighting between the two tribes of the Ansar, the Aus and Khazraj) was brought about by Allah for the good of His Apostle so that when Messenger of Allah ﷺ reached (Medina), the tribes of Medina had already divided and their chiefs had been killed and wounded. So Allah had brought about the battle for the good of H is Apostle in order that they (i.e. the Ansar) might embrace Islam.  

كَانَ يَوْمُ بُعَاثَ يَوْمًا قَدَّمَهُ اللَّهُ لِرَسُولِهِ ﷺ فَقَدِمَ رَسُولُ اللَّهِ ﷺ وَقَدِ افْتَرَقَ مَلَؤُهُمْ وَقُتِلَتْ سَرَوَاتُهُمْ وَجُرِّحُوا فَقَدَّمَهُ اللَّهُ لِرَسُولِهِ ﷺ فِي دُخُولِهِمْ فِي الإِسْلاَمِ  

Allah caused the day of Buath to take place before Messenger of Allah ﷺ was sent (as an Apostle) so that when Messenger of Allah ﷺ reached Medina, those people had already divided (in different groups) and their chiefs had been killed or wounded. So Allah made that day precede Messenger of Allah ﷺ so that they (i.e. the Ansar) might embrace Islam.  

كَانَ يَوْمُ بُعَاثٍ يَوْمًا قَدَّمَهُ اللَّهُ لِرَسُولِهِ ﷺ فَقَدِمَ رَسُولُ اللَّهِ ﷺ وَقَدِ افْتَرَقَ مَلَؤُهُمْ وَقُتِّلَتْ سَرَوَاتُهُمْ وَجُرِّحُوا قَدَّمَهُ اللَّهُ لِرَسُولِهِ ﷺ فِي دُخُولِهِمْ فِي الإِسْلاَمِ  

[Machine] It was the day of Bu'ath, a day that Allah ﷻ had prepared for His Messenger ﷺ. The Messenger of Allah ﷺ arrived in Medina, and their leaders had dispersed and their factions had been killed. They showed loyalty to Allah ﷻ and His Messenger when they entered into Islam.  

كَانَ يَوْمُ بُعَاثٍ يَوْمًا قَدَّمَهُ اللهُ ﷻ لِرَسُولِهِ ﷺ فَقَدِمَ رَسُولُ اللهِ ﷺ الْمَدِينَةَ وَقَدْ افْتَرَقَ مَلَؤُهُمْ وَقُتِلَتْ سَرَوَاتُهُمْ وَرَفَقُوا لِلَّهِ ﷻ وَلِرَسُولِهِ فِي دُخُولِهِمْ فِي الْإِسْلَامِ