Imam ‘Ali ibn Abi Talib (d. 661) was the first cousin of the Prophet Muhammad with whom he shared the same paternal grandfather, the son-in-law of the Prophet as the husband of his only surviving daughter, and the most important personality in early Islam after the Prophet himself. As noted in Sunni Muslim historical chronicles, when Imam ‘Ali was just ten years old, the Prophet Muhammad invited his close family to Islam and asked them:

Which of you, then, will help me in this, and be my brother, mine executor and my successor amongst you?’ All remained silent, except for the youthful ʿAlī who spoke up: ‘O Prophet of God, I will be thy helper in this.’ The Prophet then placed his hand on ʿAlī’s neck and said, ‘This is my brother, mine executor and my successor amongst you. Hearken unto him and obey him.’

(Ibn Ishaq, Sirat Rasul Allah [Earliest Biography of the Prophet], tr. A Guilaume, The Life of Muhammad, 118)

Ahmad al-Nasa’i, Sunan al-Kubra [one of the six canonical Sunni Hadith books], 126; Read the Arabic Text)

Shi‘a Muslims recognize Imam ‘Ali ibn Abi Talib as the temporal, religious and spiritual successor, inheritor, and legatee (wasi) of the Prophet Muhammad. Sunni Muslims recognize Imam ‘Ali as the Fourth Rightly-Guided Caliph. Sufi Muslims from both Shi‘a and Sunni traditions recognize Imam ‘Ali as the first spiritual guardian (wali) and pole (qutb) of Islamic spirituality after the Prophet Muhammad. As the husband of the Prophet’s only surviving daughter, Imam ‘Ali is the father and progenitor of all the lineal descendants of the Prophet Muhammad, including Imam al-Hasan and Imam al-Husayn and their descendants.

Although prophetic revelation (tanzil) ends with the Prophet Muhammad, the authority of spiritual guardianship (walayah), teaching (ta‘lim) and esoteric interpretation (ta’wil) continue in the person of Imam ‘Ali and his designated lineal descendants until the end of time. Imam Shah Karim al-Husayni Aga Khan IV is the 49th hereditary Imam of the Shi‘a Ismaili Muslims and the present bearer of the ‘Alid Imamat and (walayah). The Imam explained importance of Imam ‘Ali to an audience of Evangelical Christians as follows:

As you know, the Shia divided from the Sunni after the death of the Prophet Muhammad. Hazrat Ali, the cousin and son-in-law of the Prophet, was, in Shia belief, named by the Prophet to be the Legitimate Authority for the interpretation of the faith. For the Shia today, all over the world, he is regarded as the first Imam.

Mawlana Hazar Imam, Acceptance Address – Tutzing Evangelical Academy’s ‘Tolerance’ Award, May 20th, 2016

During the reign of Umayyad dynasty the family and descendants of Imam ‘Ali were heavily oppressed and the Imam ‘Ali was cursed from the pulpits of the mosques. Nevertheless, the hadith literature of the Sunni tradition of Islam has preserved numerous statements of the Prophet Muhammad where he praises the virtues, excellence and spiritual pre-eminence of Imam ‘Ali. These hadiths, either taken individually or collectively, make it abundantly clear that the Prophet had indeed appointed Imam ‘Ali as his spiritual and religious successor and as the legitimate authority for the interpretation of Islam after him. It is highly unlikely that Sunni hadiths and transmitters would have forged such statements especially given the fact of the widespread opposition to Shi‘ism. Indeed, the presence of such statements about the Imam ‘Ali’s exalted status even in Sunni literature lends support to the notion that ‘Ali was the true and legitimate successor of the Prophet Muhammad.

Before turning to the Sunni hadith, one must note that the Qur’an does refer to Imam ‘Ali in numerous verses: he is one of the Ahl al-Bayt whom God has purified from all impurity and sins (33:33) and the near-kin (qurba) of the Prophet whose love is obligatory for Muslims (42:23). Imam ‘Ali is called the Guardian (wali) of the Believers after God and the Messenger (5:55), the Witness (shahid) from the Holy Prophet who verified him (11:17), and the Guide (hadi) of the community (13:7) after the Prophet. Imam ‘Ali is part of the holy progeny of Abraham from whom God appoints the Imams (2:124) and upon whom He has bestowed His guidance, wisdom and kingdom (4:54). Imam ‘Ali is mentioned in the verse of mubahala (3:61) as the self (nafs) of the Prophet Muhammad. Verse 5:67 of the Qur’an was revealed to the Prophet Muhammad in right before the Prophet’s final announcement at Ghadeer Khum where he announced that ‘Ali is the mawla of the believers.

The hadith statements presented below appear in Reza-Shah Kazemi, Justice and Remembrance: Introducing the Spirituality of Imam ‘Ali, p. 18-20, and are accompanied here by their original references from recognized Sunni Muslim hadith books: ‘ala’l-Mustakrak al-Sahihayn by al-Hakim al-Naysaburi whose hadith isnads meet the criterion of Sahih Bukhari and Sahih Muslim, and the Khasa’is Amir al-Mu’minin ‘Ali ibn Abi Talib compiled by Ahmad b. Shu‘ayb al-Nasa’i who also authored one of the six Sunni canonical hadith collections. Later Sunni Muslim exegetes like Jalal al-Din al-Suyuti have also quoted these hadiths extensively in their works.

Truly, ‘Ali is from me and I am from him (inna ʿAlī minnī wa anā minhu), and he is the walī (patron/spiritual master) of every believer after me.

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 19, No. 4636; Ahmad b. Shu‘ayb al-Nasa’i, Khasa’is Amir al-Mu’minin ‘Ali b. Abi Talib, Tehran 1998, 129)

‘Ali is with the Qurʾān and the Qurʾān is with ‘Ali. They will not separate from each other until they return to me at the [paradisal pool] (al-ḥawḍ).

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 927, No. 4685)

[To ‘Ali]: Are you not happy that you should have in relation to me the rank of Aaron in relation to Moses, except that there is no prophet after me.

Prophet Muhammad,
(Ahmad b. Shu‘ayb al-Nasa’i, Khasa’is Amir al-Mu’minin ‘Ali b. Abi Talib, Tehran 1998, 76)

Three things were revealed to me regarding ʿAlī: he is the leader of the Muslims, the guide of the pious and chief of the radiantly devout (sayyidu’l-muslimīn, imāmu’l-muttaqīn, wa qāʾidu’l-ghurra’lmuḥajjalīn).

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 936, No. 4723)

Gazing upon ʿAlī is an act of worship (al-naẓar ilā ʿAlī ʿibāda).))

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 938, No. 4736)

May God have mercy on ʿAlī. O God, make the truth revolve around ʿAlī wherever he turns (adiri’l-ḥaqq maʿahu ḥaythu dāra)

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 927, No. 4686)

‘Ali is as my own soul (ka-nafsī).

Prophet Muhammad,
(Ahmad b. Shu‘ayb al-Nasa’i, Khasa’is Amir al-Mu’minin ‘Ali b. Abi Talib, Tehran 1998, 104)

You [‘Ali] are from me and I am from you (anta minnī wa anā minka).

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 924, No. 4672)

Whoever obeys ʿAli obeys me, and whoever disobeys him disobeys me.

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 925, No. 4678)

[To ‘Ali]: You will clarify for my community that over which they will differ after me.

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 926, No. 4678)

There is one amongst you who will fight for the taʿwīl [spiritual interpretation] of the Qurʾān as I have fought for its tanzīl [literal revelation].’ Abū Bakr asked, ‘Is it I?’. The Prophet said, ‘No’. ʿUmar asked, ‘Is it I?’. The Prophet said, ‘No, it is the one who is mending the sandal.’ The Prophet had given ʿAlī his sandal to mend.

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 926, No. 4679)

O ʿAli, whoever separates himself from me separates himself from God, and whoever separates himself from you, O ʿAli, separates himself from me.

Prophet Muhammad,
(al-Hakim al-Naysaburi, Al-Mustadrak ‘ala’l-Sahihayn, Beirut 2002, 927, No. 4682)

‘Ali is from me and I am from him (ʿAlī minnī wa anā minhu), and nobody can fulfill my duty but myself and ʿAli.

Prophet Muhammad,
(Ahmad b. Shu‘ayb al-Nasa’i, Khasa’is Amir al-Mu’minin ‘Ali b. Abi Talib, Tehran 1998, 106)

He whose mawlā [master] I am, this ʿAlī is his mawla (man kuntu mawlāhu fa-ʿAlī mawlāhu).

Prophet Muhammad,
(Cited in numerous Sunni Muslim Hadith sources listed here)

We conclude with the words of Imam Sultan Muhammad Shah Aga Khan III, the 48th hereditary Imam of the Shi‘a Ismaili Muslims:

The Khalif or successor of the Prophet was to succeed him in both these capacities; he was to be both Amir al-Mu’minin or “Commander of the true believers” and Imam-al-Muslimin or “spiritual chief of the devout.” Perhaps an analogy from the Latin, Western world will make this clearer: he would be Supreme Pontiff as well as Imperator or temporal ruler. ‘Ali, the Prophet’s cousin and son-in-law, the husband of his beloved and only surviving child, Fatimah, his first convert, his bold champion in many a war, who the Prophet in his lifetime said would be to him as Aaron was to Moses, his brother and right-hand man, in the veins of whose descendants the Prophet’s own blood would flow, appeared destined to be that true successor; and such had been the general expectation of Islam. The Shi‘as have therefore always held that after the Prophet’s death, Divine power, guidance and leadership manifested themselves in Hazrat ‘Ali as the first Imam or spiritual chief of the devout.

– Imam Sultan Muhammad Shah Aga Khan III, (Memoirs of the Aga Khan)