Musnad Ahmad 1156:12

Ibn Abi ‘Adi narrated to us, from Ibn ‘Awn, from al-Hasan, from his mother, from Umm Salamah, who said: I have not forgotten his words on the day of the Trench, while he was handing them the bricks, and the hair of his chest was covered in dust, and he was saying: "O Allah, the true life is the life of the Hereafter, so forgive the Ansar and the Muhajirun." She said: Then he saw ‘Ammar and said: "Woe to him, Ibn Sumayyah, he will be killed by the transgressing faction." He (the narrator) said: So I mentioned this to Muhammad—meaning Ibn Sirin—and he said: "From his mother?" I said: "Yes, for she used to associate with her and enter upon her."