Musnad Ahmad 28:23

Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from 'Abd al-Rahman ibn Ziyad, from 'Abd Allah ibn al-Harith, who said: I was traveling with Mu'awiyah on his return from Siffin, between him and 'Amr ibn al-'As. 'Abd Allah ibn 'Amr ibn al-'As said: "O father, have you not heard the Messenger of Allah (peace be upon him) say to 'Ammar: 'Woe to you, O son of Sumayyah, the transgressing party will kill you'?" 'Amr said to Mu'awiyah: "Do you not hear what this one is saying?" Mu'awiyah said: "You will not cease bringing us some trouble. Did we kill him? It was only those who brought him [to the battlefield] who killed him."