In January 661, Ali was assassinated by the
Kharijite Abd al-Rahman ibn Muljam. Hasan was subsequently acknowledged caliph in Kufa, the seat of Ali's caliphate. Madelung writes that Ali had apparently not nominated a successor before his sudden death but had often said that only members of Muhammad's household () were entitled to the caliphate. As Ali's legatee, Hasan must have been the obvious choice for the caliphate. Some Shia reports add that Ali also designated Hasan as his wali|, thus giving him his own authority to command, and also his , responsible for punishing his assassin. Some authors have noted that Muhammad's surviving companions were primarily in Ali's army and must have therefore pledged allegiance to Hasan, as evidenced by the lack of any reports to the contrary. of the inaugural speech of Hasan ibn Ali. In his inaugural speech at the
Great Mosque of Kufa, Hasan praised the and quoted verse 42:23 of the Quran: Ali's commander
Qays ibn Sa'd was the first to pledge his allegiance to Hasan. Qays offered his
oath based on the Quran, precedent (), and
jihad against those who declared lawful () what was unlawful (). Hasan, however, avoided the last condition by saying that it was implicit in the first two. About this episode,
Husain Mohammad Jafri () suggests that Hasan was probably already apprehensive about the Kufans' support and wanted to avoid unrealistic commitments. The oath stipulated that people "should make war on those who were at war with Hasan, and should live in peace with those who were at peace with him", writes the Sunni
al-Baladhuri (), adding that this condition astonished the people, who suspected that he intended to make peace with Mu'awiya I. In contrast, Madelung notes that the oath was identical to the one demanded earlier by Ali and denounced by the Kharijites. The view of
Maria Massi Dakake is similar.
Conflict with Mu'awiya I Having been at war with Ali, Mu'awiya I did not recognise the caliphate of his successor and prepared for war. He marched an army of sixty thousand men through
al-Jazira to Maskin, about north of the present-day
Baghdad. Concurrently, Mu'awiya I also corresponded with Hasan, urging him to give up his claim to the caliphate. Jafri suggests that he might have hoped to force Hasan to abdicate or attack the Iraqi forces before they were fortified. Mu'awiya I might have believed that Hasan would remain a threat even if he were defeated and killed, since another
Hashemite could continue the fight. If Hasan abdicated in favor of Mu'awiya I, he writes, such claims would have no weight. The view of
Momen is similar. Their letters revisit the succession of Muhammad. Hasan urged Mu'awiya I to pledge allegiance to him, using the same arguments Ali had advanced against Abu Bakr after Muhammad's death. Ali had said that if the
Quraysh could successfully claim the leadership because Muhammad belonged to them, then Muhammad's family was the most qualified to lead. Mu'awiya I replied that Muslims were not unaware of the merits of the but had selected Abu Bakr to keep the caliphate within the Quraysh. Hassan also wrote that Mu'awiya I had no true merit in Islam and was the son of Muhammad's arch-enemy
Abu Sufyan. Mu'awiya I replied that he was better suited for the caliphate because of his age, governing experience, and superior military strength, thus implying that these qualities were more important than religious precedence. Jafri comments that Mu'awiya I's response made explicit the separation of politics and religion, which later became a tenet of Sunni Islam. In contrast, Shia Islam vested all authority in the household of Muhammad.
Mobilisation of Iraqi troops Coin minted in the present-day Iran in 30 AH (661–662), during Hasan's caliphate. The Arabic phrase () appears in its margin.|alt=Coin minted during the caliphate of Hasan ibn Ali. As the news of Mu'awiya I's advance reached Hasan, he ordered his local governors to mobilise and invited the Kufans to prepare for war, "God had prescribed the jihad for his creation and called it a loathsome duty ()", referring to verse 2:216 of the Quran. There was no response at first, possibly because some tribal chiefs were bribed by Mu'awiya I. Hasan's companions now scolded the crowd and inspired them to leave in large numbers for the army campgrounds in Nukhayla. Hasan soon joined them and appointed Ubayd Allah ibn Abbas as the commander of a vanguard of twelve thousand men tasked with holding Mu'awiya I back in Maskin until the arrival of Hasan's main army. Ubayd Allah was advised not to fight unless attacked and to consult with Qays ibn Sa'd, the second in command.
Wellhausen () names
Abd Allah ibn Abbas as the commander of the vanguard, but this is rejected by Madelung, who suggests that the choice of Ubayd Allah indicates Hasan's peace intentions because the former had earlier surrendered
Yemen to Mu'awiya I without a fight. This is the view of
Ibn Shihab al-Zuhri (), the Umayyad-era historian who adopted the pro-Umayyad account that depicts a greedy Hasan eager to renounce his caliphate for money. This must have been the official Umayyad account, distributed to legitimise Mu'awiya I's rule in the absence of a council () or election or designation (), suggests Jafri.
Mutiny While the vanguard was awaiting his arrival in Maskin, Hasan faced a mutiny at his military camp near
al-Mada'in. Among the five surviving accounts, Jafri prefers the one by
Abu Hanifa Dinawari (), which states that Hasan was concerned about his troops' resolve by the time he reached the outskirts of al-Mada'in. He thus halted the army at Sabat and told them in a speech that he preferred peace over war because his men were reluctant to fight. According to
al-Mada'ini (), Hasan also quoted Ali as saying, "Do not loathe the reign of Mu'awiya I", which Madelung finds incredible. Taking the speech as a sign that Hasan intended to pursue peace,
Kharijite sympathisers in Hasan's army looted his tent and pulled his prayer rug from under him. Alternatively, Jafri and
al-Ya'qubi () hold Mu'awiya I responsible for the mutiny through his network of spies, about which letters were earlier exchanged between Mu'awiya I and Hasan and Ubayd Allah. As he was being escorted away to safety, the Kharijite al-Jarrah ibn Sinan attacked and wounded Hasan while shouting, "You have become an infidel () like your father". Al-Jarrah was overpowered and killed, while Hasan, bleeding profusely, was taken for treatment to the house of Sa'd ibn Mas'ud al-Thaqafi, the governor of
al-Mada'in. The news of this attack further demoralized Hasan's army and led to widespread desertions. Sa'd's nephew
Mukhtar ibn Abi Ubayd () reportedly recommended the governor to surrender Hasan to Mu'awiya I but was rejected.
Desertions The Kufan vanguard arrived in Maskin and found Mu'awiya I, who was camped there. Through a representative, he urged them not to commence hostilities until he concluded his peace talks with Hasan. This was likely a false claim. The Kufans, however, insulted Mu'awiya I's envoy and sent him back. Mu'awiya I then sent an envoy to visit Ubayd Allah privately, telling him that Hasan had requested a truce, and then offered him a million dirhams to switch sides. Ubayd Allah accepted and deserted at night to Mu'awiya I, who fulfilled his promise to him. The next morning, Qays ibn Sa'd took charge of Hasan's troops as the second-in-command and denounced Ubayd Allah in a sermon. Mu'awiya I now sent a contingent to force surrender, but was pushed back twice. He then offered bribes to Qays in a letter, which he refused. As the news of the mutiny against Hasan and the attempt at his life arrived, however, both sides abstained from fighting and awaited further developments. Veccia Vaglieri writes that the Iraqis were reluctant to fight and that a group deserted every day. By one account, 8,000 men out of 12,000 followed Ubayd Allah's example and joined Mu'awiya I. When Hasan learned about this, al-Ya'qubi writes that he summoned the Iraqi nobles and reproached them for their unreliability and fickle-mindedness, echoing the speeches of Ali after Siffin.
Treaty with Mu'awiya I Mu'awiya I now sent envoys to propose that Hasan abdicate in his favor to spare Muslim blood. In return, Mu'awiya I was ready to designate Hasan as his successor, grant him safety, and offer him a large financial settlement. Hasan accepted the overture in principle and sent his representative(s) to Mu'awiya I, who sent them back to Hasan with
carte blanche, inviting him to dictate whatever he wanted. Hasan wrote that he would surrender the Muslim rule to Mu'awiya I if he would comply with the Quran and , that his successor would be appointed by a council (
shura), that the people would remain safe, and that Hasan's supporters would receive amnesty. His letter was witnessed by two representatives, who carried it to Mu'awiya I. Hasan thus renounced the caliphate in August 661 after a seven-month reign. This year is considered by a number of the early Muslim sources as "the year of unity" and is generally regarded as the start of Mu'awiya I's caliphate.
Terms of the treaty Veccia Vaglieri finds certain variants of the treaty impossible to reconcile. She lists several conditions in the early sources and questions their veracity, including an annual payment of one or two million dirhams to Hasan, a single payment of five million dirhams from the treasury of Kufa, annual revenues from variously named districts in
Persia, succession of Hasan to Mu'awiya I or a council () after Mu'awiya I, and preference for the
Banu Hashim over the
Banu Umayyad in pensions. Another condition was that Mu'awiya I should end the ritual cursing of Ali in mosques, writes Mavani. Jafri similarly notes that the terms are recorded differently and ambiguously by al-Tabari, Dinawari, Ibn Abd al-Barr, and Ibn al-Athir, while al-Ya'qubi and
al-Masudi () are silent about them. In particular, Jafri finds the timing of Mu'awiya I's
carte blanche problematic in al-Tabari's account. Al-Tabari also mentions a single payment of five million dirhams to Hasan from the treasury of Kufa, which Jafri rejects because the treasury of Kufa was already in Hasan's possession at the time. He adds that Ali regularly emptied the treasury and distributed the funds among the public, and this is also reported by Veccia Vaglieri. Jafri then argues that the most comprehensive account is the one given by
Ahmad ibn A'tham, probably taken from al-Mada'ini, who recorded the terms in two parts. The first part is the conditions proposed by Abd Allah ibn Nawfal, who negotiated on Hasan's behalf with Mu'awiya I in Maskin. The second part is what Hasan stipulated in
carte blanche. These two sets of conditions together encompass all the conditions scattered in the early sources. Jafri thus concludes that Hasan's final conditions in
carte blanche were that Mu'awiya I should act according to the Quran, , and the conduct of the
Rashidun caliphs, that the people should remain safe, and that the successor to Mu'awiya I should be appointed by a council. These conditions are echoed by Madelung, who adds that Hasan made no financial stipulations in his peace proposal and Mu'awiya I consequently made no payments to him, contrary to the "Umayyad propaganda" reflected in the account of al-Zuhri, quoted by al-Tabari. Since Ali and his house rejected the conduct of Abu Bakr and Umar in the
after Umar in 23/644, Jafri believes that the clause about following the Rashidun caliphs was inserted by later Sunni authors. That Mu'awiya I agreed to an amnesty for the supporters of Ali indicates that the revenge for Uthman was a pretext for him to seize the caliphate, according to Jafri.
Abdication In the surrender ceremony, Mu'awiya I demanded that Hasan publicly apologise. Hasan rose and reminded the people that he and Husayn were Muhammad's only grandsons, that the right to the caliphate was his and not Mu'awiya I's, but that he had surrendered it to avoid bloodshed. Mu'awiya I then spoke and recanted his earlier promises to Hasan and others, saying that those promises were made to shorten the war. As reported by the Mu'tasilite
Ibn Abi'l-Hadid () and
Abu al-Faraj al-Isfahani (), Mu'awiya I added that he had not fought the Iraqis so that they would practice Islam, which they were already doing, but to be their master (amir|). Al-Baladhuri writes that Mu'awiya I then gave the Kufans three days to pledge allegiance or be killed. After this, the people rushed to vow allegiance to Mu'awiya I. Hasan left Kufa for Medina but soon received a request from Mu'awiya to subdue a Kharijite revolt near Kufa. He wrote back to Mu'awiya I that he had given up his claim to the caliphate for the sake of peace and compromise, not to fight on his side.
Retirement Between his abdication in 41/661 and his death in 50/670, Hasan lived quietly in Medina and did not engage in politics. In compliance with the peace treaty, Hasan declined requests from (often small) Shia groups to lead them against Mu'awiya I. He was nevertheless considered the head of the house of Muhammad by the Banu Hashim and Ali's partisans, who had probably pinned their hopes on his succession to Mu'awiya. The Sunni al-Baladhuri in his
Ansab writes that Hasan sent tax collectors to the Fasa and Darabjird provinces of Iran in accordance with the treaty, but the governor of Basra, instructed by Mu'awiya I, incited the people against Hasan, and his tax collectors were driven out of the two provinces. Madelung regards this account as fictitious because Hasan had just refused to join Mu'awiya I in fighting the Kharijites. He adds that Hasan had made no financial stipulations in his peace proposal, and Mu'awiya I consequently made no payments to him. Madelung suggests that the relations between the two men deteriorated when Mu'awiya I realised that Hasan would not actively support his regime. == Death ==