It is a fact that the religion of the Imamites is same as the religion of Ahlul Bayt (a.s.), and it is absolutely different from the religion of Ahlul Sunnat. As mentioned by Sharif Zurjani in Sharh Mawaqif: Initially the Imamites followed the religion of their Imams, but after a long time controversies developed among them.
The descendants of Ahlul Bayt (a.s.) (Sadaat) were indeed initially on the religion of their Imams, but the passage of time changed their faiths. Today they follow every type of religion, some are Shias and some Tafzeeliya, some Sunni, some Wahabi, Khariji, Nasibi, Christian and some are even atheists. We should know that society and government has a great influence on religion.
Some Sadaats in India are seen following a religion of other than the Imamites. This is so, because India mostly had non-Shia rulers. Economic and monetary factors forced the Sadaat of India to start following the religion of the rulers and this deprived their families of the religion of their forefathers. Now these poor people do not even know what religion their forefathers had followed, or whether their present religion is new or ancient. The statement of the writer of Al Milal wan Nihal also proves that the Imams of Ahlul Bayt (a.s.) had a distinct religion. And their followers were called Imamites as they also followed the same faith.
Ibn Kathir, a great Sunni scholar, writes the following in connection with the Imamite faith in his book Jame al-Usool: “Now we describe the well known faiths of the Muslims that were followed by the people in different areas of the world. That is the Shafei, the Hanafite, the Maliki, the Hanbali and the Imamiyah.” After this, the respected scholar has named and introduced the founders of each of these faiths. Regarding the founders of Imamiyah faith, he writes:
“The leader of the Imamiyah in the second century was Ali Ibn Moosa ar-Reza and in the third century, it was Muhammad Ibn Yaqoob al-Kulaini and in the fourth century it was Sayyid Murtada Alamul Huda. The religion of all the Ahlul Bayt (a.s.) was same. Thus, whatever was the religion of Ali Ibn Moosa ar- Reza, it was the same religion of all the Imams.”