Quran and the authentic orders of the Prophet Muhammad (SAWA) are the main evidence that the real Islam is the Islam of Ahlul Bayt (AS) and Shia Muslims are the followers of Ahlul Bayt (AS), which means that the real Islam is what is called Shia Islam.
Allah in Quran has ordered the absolute obedience to Allah, the messenger and the divine leaders (Sura 4, verse 59). Absolute obedience can never to fallible persons. The order means that the absolute obedience to Allah, the messenger and the divine leaders from Ahlul Bayt (AS) about whom the Prophet Muhammad (SAWA) ordered Muslims to follow and absolutely obey. He said : I am leaving among you two most important things that you will never go astray if you keep following them; the book of Allah and my Progeny Ahlul Bayt (Saheeh Muslim, Hadeeth number 4425, Sunan al-Tirmithi 3718, and 3720, al-Mustadrak by Nisabori 4576 and 4577 and many other references in Sunni books.
The Prophet Muhammad (SAWA) announced in the day of Ghadeer the leadership of Ali after him as it is narrated in hundreds of Sunni books, and Shia Muslims are obeying the order of the Prophet in this most important matter and every matter.
Shia Muslims take the meanings of Quran (Tafseer) and the Sunnah from the most knowledgeable and most pious who are Ahlul Bayt (AS) as they were been ordered by the Prophet himself (SAWA).