I asked Anas, "Tell me about the name 'Al-Ansar.; Did you call yourselves by it or did Allah call you by it?" He said, "Allah called us by it." We used to visit Anas (at Basra) and he used to narrate to us the virtues and deeds of the Ansar, and he used to address me or a person from the tribe of Al-Azd and say, "Your tribe did so-and-so on such-and-such a day."  

قُلْتُ لأَنَسٍ أَرَأَيْتَ اسْمَ الأَنْصَارِ كُنْتُمْ تُسَمَّوْنَ بِهِ أَمْ سَمَّاكُمُ اللَّهُ قَالَ بَلْ سَمَّانَا اللَّهُ كُنَّا نَدْخُلُ عَلَى أَنَسٍ فَيُحَدِّثُنَا مَنَاقِبَ الأَنْصَارِ وَمَشَاهِدَهُمْ وَيُقْبِلُ عَلَىَّ أَوْ عَلَى رَجُلٍ مِنَ الأَزْدِ فَيَقُولُ فَعَلَ قَوْمُكَ يَوْمَ كَذَا وَكَذَا كَذَا وَكَذَا  

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  

On the day of the Conquest of Mecca, when the Prophet ﷺ had given (from the booty) the Quraish, the Ansar said, "By Allah, this is indeed very strange: While our swords are still dribbling with the blood of Quraish, our war booty are distributed amongst them." When this news reached the Prophet ﷺ he called the Ansar and said, "What is this news that has reached me from you?" They used not to tell lies, so they replied, "What has reached you is true." He said, "Doesn't it please you that the people take the booty to their homes and you take Messenger of Allah ﷺ to your homes? If the Ansar took their way through a valley or a mountain pass, I would take the Ansar's valley or a mountain pass."  

قَالَتِ الأَنْصَارُ يَوْمَ فَتْحِ مَكَّةَ وَأَعْطَى قُرَيْشًا وَاللَّهِ إِنَّ هَذَا لَهُوَ الْعَجَبُ إِنَّ سُيُوفَنَا تَقْطُرُ مِنْ دِمَاءِ قُرَيْشٍ وَغَنَائِمُنَا تُرَدُّ عَلَيْهِمْ فَبَلَغَ ذَلِكَ النَّبِيَّ ﷺ فَدَعَا الأَنْصَارَ قَالَ فَقَالَ مَا الَّذِي بَلَغَنِي عَنْكُمْ وَكَانُوا لاَ يَكْذِبُونَ فَقَالُوا هُوَ الَّذِي بَلَغَكَ قَالَ أَوَلاَ تَرْضَوْنَ أَنْ يَرْجِعَ النَّاسُ بِالْغَنَائِمِ إِلَى بُيُوتِهِمْ وَتَرْجِعُونَ بِرَسُولِ اللَّهِ ﷺ إِلَى بُيُوتِكُمْ لَوْ سَلَكَتِ الأَنْصَارُ وَادِيًا أَوْ شِعْبًا لَسَلَكْتُ وَادِيَ الأَنْصَارِ أَوْ شِعْبَهُمْ