[1] Ali frequently accused the third caliph, Uthman, of deviating from the Quran and the Sunna,[4][5][6] and was joined in his criticism by most of the senior companions of the Islamic prophet Muhammad, including Talha and Zubayr.

Among other Western historians, Giorgio Levi della Vida (d. 1967) is unsure, while Wilferd Madelung strongly rejects the accusation, saying that it "stretches the imagination" in the absence of any evidence.

[27][5] In turn, their opinion is challenged by Madelung, who argues that Aisha would have not actively opposed Uthman if Ali had been the prime mover of the rebellion and its future beneficiary.

[113] Mu'awiya also brought into his camp the influential Syrian Shurahbil ibn Simt,[1] whom he convinced that Ali was guilty in the death of Uthman,[114][115] probably with false witnesses and reports.

[117] Madelung similarly writes that al-Miswar ibn Makhrama refused to support Mu'awiya on behalf of the holy cities, asking him in a letter what a taliq whose father had led the confederate armies against Muslims had to do with the caliphate.

[116] Mu'awiya did, however, win to his side Ubayd Allah, son of the second caliph Umar and a triple murderer, who had fled after learning that Ali intended to apply the lex talionis to him.

[129] Other modern authors similarly tend to consider Mu'awiya's call for revenge as a guise,[130][131][132][133][81][122] intended initially to maintain his rule over Syria,[133][28] or to seize the caliphate altogether later.

[81] Some authors instead regard the call for revenge as a pious cloak for broader issues: Hinds and Poonawala trace back Mu'awiya's revolt to his demands to rule over an autonomous Syria,[136][28] which was kept free (unlike Iraq) from uncontrolled immigration to check the Byzantine threats.

[139] As for whether and when Mu'awiya first aspired to the caliphate,[140] it is the conclusion of Ayoub that he might have had two scenarios in mind: The first one was keeping the rule of Syria and annexing Egypt, as he indeed proposed to Ali's envoy, Jarir.

[142][143][65] While he did not condone the assassination,[144] Ali probably held Uthman responsible through his injustice for the protests that led to his death,[142][145] a view for which Poonawala cites Waq'at Siffin.

[151] Quoting al-Ya'qubi and al-Kufi, Ayoub suggests that a mob from various tribes murdered Uthman and that Ali could have not punished them without risking widespread tribal conflict, even if he could identify them.

[106] At the time, Mu'awiya was also repeatedly accused of abandoning Uthman during the deadly siege of his residence,[129] and this view is echoed by the Islamic author Hassan Abbas and by the Shia scholar Muhammad H. Tabatabai (d. 1981).

[163][134] Similarly, a letter ascribed to the besieged Uthman by al-Tabari and al-Ya'qubi alleges that Mu'awiya deliberately withheld the requested reinforcements to benefit politically from the caliph's death.

[65] As for the public, the Kufans were not united in supporting the war, either simply because of its expected toll,[167][1] or because they were reluctant to shed other Muslims' blood,[3][100] or perhaps because the Syrians had never pledged allegiance to Ali in the first place,[167][138] even though similar cases were judged to be apostasy by Abu Bakr.

[174][137] He left the protection of his western borders to three local Palestinian commanders, probably because Muhammad ibn Abu Bakr faced internal problems as Ali's new governor in Egypt.

[175] Siffin is described in Arabic sources as a conflict between the people of Iraq and Syria,[158][126] in which most tribes were represented on both sides,[158] such as the Banu Kath'am, which was divided to Iraqi and Syrian branches.

The former also promised better material benefits to tribal leaders compared to Ali, who applied strict measures to governors who embezzled money, and this in turn led to their defection to Mu'awiya's side.

[180] To illustrate the division among Kufans, Ayoub cites an account by Ibn Muzahim to the effect that some asked Ali for permission to accompany his army without engaging in battle until they made up their minds.

[200][201] According to the same source, also around the same time did Mu'awiya send his brother Utba to negotiate a separate truce with al-Ash'ath ibn Qays, the influential Yemenite tribal leader, who was not closely associated with Ali or his cause.

Then during the Battle of the Camel, Ka'b ibn Sur al-Azdi, the judge (qadi) of Basra, who counted among the rebels, walked to the battlefield with a copy of the Quran and pleaded for the fighting to stop.

[214] This account is also what John Kelsay and Reza Aslan prefer,[153] with the latter saying that most of his men pleaded with Ali to ignore the call to arbitration but he accepted it and cited the Quranic verse 2:193, "if [the enemy] desists, then you must also cease hostilities.

[103] Jafri further suggests that the Kufan tribal leaders probably resented the egalitarian policies of Ali, as he divided the treasury funds equally among Arabs and non-Arabs, and among late- and new-comers to Kufa.

[239][65] Veccia Vaglieri and Rahman write that the Iraqis were so convinced of the legitimacy of their cause that they insisted on the neutral Abu Musa,[209][245] whereas others suggest that they were impressed by his piety,[100] or his beautiful recitations of the Quran,[122] or that he stood for provincial autonomy in Kufans' view.

[240] The two representatives committed to meet on neutral territory,[126] to adhere to the Quran and Sunna and to save the community from war and division,[233][130] a clause added evidently to appease the peace party.

[259] Many of the dissidents apparently accepted Ali's position,[253] while the rest left for al-Nahrawan, a town near al-Mada'in, and there declared Abd-Allah ibn Wahb al-Rasibi (d. 658) as their leader.

[254] Alternatively, Hinds and Poonawala believe that the seceders were disillusioned with the arbitration process, particularly by the removal of Ali's title of amir al-mu'minin in the final agreement and by its reference to the Sunna next to the Quran,[266][28] as noted also in Waq'at Sifin.

[273] Nevertheless, after some months of preparation, or perhaps even a year after the initial agreement,[274] it appears that the two arbitrators met together, first in Dumat al-Jandal, halfway between Iraq and Syria,[258] and then in Udhruh,[275][28] in southern Palestine.

[277] Madelung views the verdict about Uthman as a political one, a judicial misjudgment, and a blunder of the naive Abu Musa, who might have hoped that Amr would later reciprocate his concession.

[288] As for the final scene of the Udhruh meeting, one popular account is that Abu Musa deposed both Ali and Mu'awiya and called for a council to appoint the new caliph per his earlier agreement with Amr.

[290] The Kufan delegation then reacted furiously to Abu Musa's concessions,[282] and he fled to Mecca in disgrace, whereas Amr was well-received by Mu'awiya upon his return to Syria.