Musnad Ahmad 771:37

Hassan ibn Musa narrated to us, Hammad ibn Salamah narrated to us, from Ali ibn Zayd, from an-Nadr ibn Anas, that Zayd ibn Arqam wrote to Anas ibn Malik during the time of al-Harrah, consoling him regarding those who were killed from his children and his people. He said: "I bring you glad tidings from Allah, the Almighty and Majestic. I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'O Allah, forgive the Ansar, and the children of the Ansar, and the children of the children of the Ansar. And forgive the women of the Ansar, and the women of the children of the Ansar, and the women of the children of the children of the Ansar.'"