Musnad Abu Ya'la al-Mawsili 244:16

Isma'il ibn Musa, the son of the daughter of al-Suddi, narrated to us, Asbat ibn Muhammad narrated to us, from al-A'mash, from 'Abd al-Rahman ibn Abi Ziyad, from 'Abd Allah ibn al-Harith ibn Nawfal, who said: I returned with Mu'awiyah from Siffin. Mu'awiyah and Abu al-A'war al-Sulami were traveling on one side, and I saw [the followers of] 'Ali traveling on the other side. I was between them, and there was no one else besides me. Sometimes I would urge my mount toward these, and sometimes I would urge my mount toward those. I heard 'Abd Allah ibn 'Amr say to his father: "O father, did you not hear the Messenger of Allah (peace be upon him) say to 'Ammar when he was building the mosque: 'You are indeed eager for the reward'?" He said: "Yes." He said: "And you are among the people of Paradise, and the transgressing faction will kill you." He said: "Yes, I have heard it." He said: "Then why did you kill him?" He said: Mu'awiyah turned to me and said: "O Abu 'Abd al-Rahman, do you not hear what this one is saying?" He [the son] said: "Did you not hear the Messenger of Allah (peace be upon him) say to 'Ammar while he was building the mosque: 'Woe to you, you are indeed eager for the reward, and the transgressing faction will kill you'?" He said: "Yes, I have heard it." He said: "Then why did you kill him?" He said: "Woe to you, you continue to slip in your own urine! Did we kill him? Only the one who brought him killed him."