—he dismissed him and appointed al-Mughīra ibn Shuʿba.

In Ahmad’s Musnad it is related through the chain: Yazīd narrated to us, al-ʿAwwām informed us, Aswad ibn Masʿūd told me, from Hanẓala ibn Khuwaylid al-ʿAnbarī, who said:
“While I was sitting with Muʿāwiyah, two men came to him disputing over ʿAmmār’s head, each saying, ‘I killed him.’ ʿAbd Allah ibn ʿAmr said, ‘Let one of you gladly yield the claim to the other, for I heard the Messenger of Allah ﷺ say: “The rebellious party will kill him.”’
Muʿāwiyah retorted, ‘O ʿAmr! Will you not rid us of your madman? Why have you brought him along with us?’
ʿAbd Allah replied, ‘My father complained about me to the Messenger of Allah ﷺ, and he said, “Obey your father as long as he is alive.” That is why I am with you, but I am not fighting.’ (1)

Nāfiʿ ibn ʿUmar narrated, from Ibn Abī Mulaykah, that ʿAbd Allah ibn ʿAmr (may Allah be pleased with him) said: ‘What have I to do with Ṣiffīn? What have I to do with fighting Muslims? I would have wished that I had died twenty years before it—or, he said, ten years. By Allah, even so I neither struck with a sword nor shot an arrow.’
It was also mentioned that the banner had been in his hand. (2)

Yazīd ibn Hārūn narrated to us; ʿAbd al-Malik ibn Qudāmah narrated; ʿAmr ibn Shuʿayb narrated from his father, from his grandfather:
His father ʿAmr said to him on the Day of Ṣiffīn, ‘Go out and fight.’
He answered, ‘Father, how can you order me to go out and fight when you yourself heard from the Messenger of Allah ﷺ what you heard about me?’
His father said, ‘I adjure you by Allah! Do you know that the last thing the Messenger of Allah ﷺ said to you was that he took your hand, placed it in mine, and said, “Obey ʿAmr ibn al-ʿĀṣ as long as he lives”?’
He replied, ‘Yes.’
He said, ‘Then I command you to fight.’ (3)