Musannaf Ibn Abi Shayba 38:117

Yahya ibn Adam narrated to us, he said: Ibn ‘Uyaynah narrated to us, from ‘Asim ibn Kulayb al-Jarmi, from his father, who said: I was exiting the mosque when I saw Ibn ‘Abbas when he came from Mu’awiyah regarding the matter of the two arbitrators. He entered the house of Sulayman ibn Rabi’ah, and I entered with him. A man kept throwing at him, then another man after another man, "O Ibn ‘Abbas, you have disbelieved, and associated partners, and set up rivals! Allah said in His Book such and such, and Allah said such and such, and Allah said such and such," until that entered into me [i.e., I became distressed by it]. He [Ibn ‘Abbas] said: "And who are they? By Allah, they are the first generation, the companions of Muhammad. By Allah, they are the companions of the burnouses and the pillars." He [the narrator] said: Ibn ‘Abbas then said, "Look for your most argumentative, your most disputatious, and your most knowledgeable of your proof, so that he may speak." So they chose a one-eyed man called ‘Attab, from the tribe of Taghlib. He stood up and said, "Allah said such and such, and Allah said such and such," as if he were plucking his need from the Qur’an in a single surah. Ibn ‘Abbas said, "I see that you are a reader of the Qur’an, knowledgeable of what you have separated and joined. I adjure you by Allah, besides whom there is no god, do you know that the people of Syria asked for the arbitration, and we disliked it and refused it? Then, when the wounds afflicted you, and the pain bit you, and you were prevented from the water of the Euphrates, you began seeking it. Mu’awiyah informed me that he was brought a horse with a belly far from the ground to flee upon it, then someone from you came to him and said, 'I left the people of Iraq surging like the people on the night of departure in Makkah, saying things, differing in every direction, like the night of departure in Makkah.'" Ibn ‘Abbas then said, "I adjure you by Allah, besides whom there is no god, what kind of man was Abu Bakr?" They said, "The best," and they praised him. He said, "Have you considered if a man went out for Hajj or ‘Umrah and struck a gazelle or some of the vermin of the earth, and one of them judged regarding it alone—would he have the right, while Allah says: 'Two just men from among you shall judge it'? So what you have differed over regarding the affair of the Ummah is greater." He said, "So do not deny two arbitrators regarding the blood of the Ummah, when Allah has placed two arbitrators in the killing of a bird, and has placed two arbitrators between the disagreement of a man and his wife, to establish justice and fairness between them in what they differed over."