And in another place...

And in another place: 'If anyone desires (to follow) a faith other than Islam, (fa lan yuqbala minhu) never will it be accepted of him and in the Hereafter he will be in the ranks of those who are lost' (3:85). Most importantly, the final revelation from Allah to the Prophet took place at Ghadir and the fate of the salvation of mankind is sealed in Islam.

The revelation is clear and leaves no doubt about Allah's seal over Islam: 'This day have I perfected your religion for you, completed My Favour upon you, and have chosen for you Islam as your faith' (5:3). Ghadir's theology is therefore very interesting and must be seen in its true perspective. Islam believes that all prophets were Muslims[^2]. By this doctrine, they gave a clear message to worship only One God, Allah.

They each proclaimed their prophethood and they each warned about the impending Day of Judgement. Since the prophethood had not yet ended, they also declared about the advent of the final Prophet;[^3] with whom not only would end the prophethood but also, as is obvious, the process of revelation. Henceforth, there would be no revelation and no new scripture.

The Qur'an, therefore, would be protected by Allah Himself so that no one would ever tamper with it.[^4] One reason for Allah's guarantee of the Qur'an's protection is that together with the 'Itrat of the Prophet, it would act as al-thaqal aI-akbar (the weightiest or the heaviest) force in guiding mankind in the absence of the Prophet.

This is clear also from the hadith of Al-Thaqalayn.[^5] The prime duty of the 'Itrat of the Prophet would be to uphold the injunctions of the Qur'an and disallow any innovations or schisms in the Sunnah of the Prophet.[^6] The duty to uphold these would remain in the hands of an Imam who would be endowed with 'ilm and be appointed through the process of nass.

Since humanity henceforth would be guided by the Qur'an and the Sunnah under an Imam and since the immediate Imam after the demise of the Prophet would be Imam Ali, upon whom be peace, the Prophet has shown Imam Ali as his clear successor throughout his mission leading up to the event of Ghadir Khumm. As we shall see, that in doing so, the Prophet was clearly charting the principles of the Usul-e Din to be followed.

There are several incidents recorded in all authentic sources - both Shi'i as well as Ahlul Sunnat wa al-Jama'ah (Sunni) - where the Prophet advanced Imam Ali to indicate his wilaya over all others.