ʿAbdullah 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 Messenger of Allah ﷺ saying, O Allah! Forgive the Ansar and the Ansar children.
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۔»