Sahih Bukhari Volume 5, Book 64, Hadith 4080

حَدَّثَنِي عَمْرُو بْنُ عَلِيٍّ، حَدَّثَنَا مُعَاذُ بْنُ هِشَامٍ، قَالَ حَدَّثَنِي أَبِي، عَنْ قَتَادَةَ، قَالَ مَا نَعْلَمُ حَيًّا مِنْ أَحْيَاءِ الْعَرَبِ أَكْثَرَ شَهِيدًا أَعَزَّ يَوْمَ الْقِيَامَةِ مِنَ الأَنْصَارِ‏.‏ قَالَ قَتَادَةُ وَحَدَّثَنَا أَنَسُ بْنُ مَالِكٍ أَنَّهُ قُتِلَ مِنْهُمْ يَوْمَ أُحُدٍ سَبْعُونَ، وَيَوْمَ بِئْرِ مَعُونَةَ سَبْعُونَ، وَيَوْمَ الْيَمَامَةِ سَبْعُونَ، قَالَ وَكَانَ بِئْرُ مَعُونَةَ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم، وَيَوْمُ الْيَمَامَةِ عَلَى عَهْدِ أَبِي بَكْرٍ يَوْمَ مُسَيْلِمَةَ الْكَذَّابِ‏

Narrated By Qatada : We do not know of any tribe amongst the 'Arab tribes who lost more martyrs than Al-Ansar, and they will have superiority on the Day of Resurrection. Anas bin Malik told us that seventy from the Ansar were martyred on the day of Uhud, and seventy on the day (of the battle of) Bir Ma'una, and seventy on the day of Al-Yamama. Anas added, "The battle of Bir Ma'una took place during the lifetime of Allah's Apostle and the battle of Al-Yamama, during the caliphate of Abu Bakr, and it was the day when Musailamah Al-Kadhdhab was killed."