The religion of God does not know by the men, but by verse of the right, learn the right to know its men.
Question:
Which Islam is correct? Which Islam should we believe in? Islam of Isis, Taliban, Shia, or Sunni etc?
Answer:
First: amir al-mu'minin Imam Ali (A) answers:
"The religion of God does not know by the men, but by verse of the right, learn the right to know its men." [1]
Second: the water that comes from spring may inter ten paths in which may be polluted by other things. And if we want to have the pure water of spring, we should go straight to the headwater. Headwater of Islam is Revelation that has revealed from Allah the almighty to the Prophet (S), and this revelation as it called as the holy Qur'an is still with us. Of course with the dirty hands or polluted dishes we can't expect to benefit from the same pure water. So when we refer to the holy Qur'an, we have to empty our mind from any prejudice and short-sighted analyses. But not all of our needs are met at the headwater, and some reasons make us utilize the water in other forms. This is where the infallible Commentators of the Qur'an are available.
Note:
[1] Sulaim b. Ghais al-hilali, v.1, p.157: "إنّ دين اللّه لا يعرف بالرجال بل بآية الحقّ، فاعرف الحقّ تعرف أهله"