Musnad Abu Ya'la al-Mawsili 105:44

Al-Qawariri narrated to us, Khalid bin al-Harith narrated to us, Ibn 'Awn narrated to us, from al-Hasan, who said: Umm Hasan said: The Mother of the Believers, Umm Salamah, said: I have not forgotten the day of the Trench, while he (the Prophet, peace and blessings of Allah be upon him) was handing them the milk, and his hair had become dusty, and he was saying: "Indeed, the true good is the good of the Hereafter, so forgive the Ansar and the Muhajirah." Then Ammar came, and he (the Prophet) said: "Woe to you" — or "Alas for you" (Khalid bin al-Harith was uncertain) — "O son of Sumayyah, the rebellious group will kill you." Ibn 'Awn said: I narrated to Muhammad from his mother, and he said: "Indeed, she used to enter upon Umm Salamah."