Wa`alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

In the Name of Allah, Most Gracious, Most Merciful.

All praise and thanks are due to Allah, and peace and blessings be upon His Messenger. 

Thank you, brother, for your question, which reflects your desire to understand the teachings of Islam. We implore Allah to guide us all to the best and to grant Muslims every success, power, and strength. 

In times of crisis, it is very important that all Muslims forget their differences and cooperate to serve the common cause of Islam against the challenges facing the Muslim Ummah. It is the duty of all Muslims to defend Islam, enjoin what is good, and forbid what is evil. 

In his response to your question, the prominent Muslim scholar Sheikh Muhammad Iqbal Nadvi, director and imam of Al-Falah Islamic Center, Oakville, Ontario, Canada, states the following:

First of all, we should understand that we have differences with the Shi`a but they are considered Muslims. Even though the Shiite school has differences in some secondary issues of `aqeedah and many issues in fiqh, they still believe that Allah is One and that Muhammad is the Messenger of Allah, and in other essentials of Islam.

To declare someone kafir needs a very clear proof for it. In most cases in the Shi`a sect, the controversial issues are based on ta'weel, which means to explain things outside their contexts. So the majority of Sunni scholars have agreed that if someone used a wrong ta'weel, it will be wrong but it does not lead to kufr (disbelief).

As for cooperation with Shiites, it is very important that we Muslims, Sunnis and Shiites, cooperate and join together to serve the common cause of Islam. We should brush aside our differences in order to stand together against the challenges facing the Muslim Ummah. It is the duty of both the Sunnis and the Shiites to defend Islam, enjoin what is good, and forbid what is evil. Cooperating on common grounds does not mean to convert from Sunni to Shi`a or vice versa, but to stand together to achieve what we both agree upon and excuse ourselves for issues that we differ about.