Narrated Musa bin 'Uqba:

'Abdullah bin Al-Fadl told me that Anas bin Malik said, "I was much grieve over those who had been killed in the Battle of Al-Harra. When Zaid bin Arqarr heard of my intense grief (over the killed Ansar), he wrote a letter to me saying that he heard Allah's Apostle saying, O Allah! Forgive the Ansar and the Ansar children. The subnarrator, Ibn Al-Fadl, is not sure whether the Prophet also said, And their grand-children." Some of those who were present, asked Anas (about Zaid). He said, "He (Zaid) is the one about whom Allah's Apostle ﷺ said, 'He is the one whose sound hearing Allah testified.'

حَدَّثَنَا إِسْمَاعِيلُ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنِي إِسْمَاعِيلُ بْنُ إِبْرَاهِيمَ بْنِ عُقْبَةَ، عَنْ مُوسَى بْنِ عُقْبَةَ، قَالَ حَدَّثَنِي عَبْدُ اللَّهِ بْنُ الْفَضْلِ، أَنَّهُ سَمِعَ أَنَسَ بْنَ مَالِكٍ، يَقُولُ حَزِنْتُ عَلَى مَنْ أُصِيبَ بِالْحَرَّةِ فَكَتَبَ إِلَىَّ زَيْدُ بْنُ أَرْقَمَ وَبَلَغَهُ شِدَّةُ حُزْنِي يَذْكُرُ أَنَّهُ سَمِعَ رَسُولَ اللَّهِ ﷺ يَقُولُ " اللَّهُمَّ اغْفِرْ لِلأَنْصَارِ وَلأَبْنَاءِ الأَنْصَارِ " ـ وَشَكَّ ابْنُ الْفَضْلِ فِي أَبْنَاءِ أَبْنَاءِ الأَنْصَارِ ـ فَسَأَلَ أَنَسًا بَعْضُ مَنْ كَانَ عِنْدَهُ فَقَالَ هُوَ الَّذِي يَقُولُ رَسُولُ اللَّهِ ﷺ " هَذَا الَّذِي أَوْفَى اللَّهُ لَهُ بِأُذُنِهِ ".