According to consecutively narrated traditions...
According to consecutively narrated traditions, the conditions of the Imam, which tribe he is from, and the fact that the number of Imams (peace be upon them) is twelve all have been explained by the Holy Prophet (peace be upon him and his family).
Similarly, the qualities of the Imam’s knowledge, his spiritual characteristics, and that he must be the most knowledgeable and perfect of all human beings have been explained in the Qur’an and traditions, as has the fact that the successorship of the Holy Prophet (peace be upon him and his family) and Imamat e of the ummah after him is a Divine post that, just like prophethood itself, is appointed by Allah.
Shi‘a thought was established in the very first years of the advent of Islam on the basis of the original sources of Islam. However, at that time the opposing school of thought – which some time later came to be known as Sunni thought – did not exist and the Muslims were not divided into two branches.
This is because those who, after the Prophet’s (peace be upon him and his family) death, propagated the opposing view – which caused a division in the Muslim ranks – were unable to openly position themselves against the pure Islam, which later came to be known as Shi‘a Islam. This division officially became apparent after the Holy Prophet (peace be upon him and his family) when a group gathered in Saqifah and chose a successor for the Holy Prophet (peace be upon him and his family).
“Although, were they to refer that to the Messenger (peace be upon him and his family) and those in authority among them, those among them who understand the roots of the issues would know it. ”[^2] From this verse, it is understood that leadership is exclusive to the Holy Prophet (peace be upon him and his family) and the ulu ‘l-amr , who are the infallible Imams.
According to mutawatir traditions, the Holy Prophet (peace be upon him and his family) has clearly introduced this virtuous authority, which is none other than the progeny and Imams from the Ahl al-Bait of the Holy Prophet (peace be upon him and his family).