Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that when news reached Sayyiduna Zayd bin Arqam (may Allah be pleased with him) of my grief over those of my people who were martyred in the incident of al-Harrah, he wrote to me that he had heard the Messenger of Allah (peace and blessings be upon him) saying: "O Allah, forgive the Ansar and the children of the Ansar." (The narrator) Ibn al-Fadl was in doubt about the words "the children of the children of the Ansar."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4953