Despite the real diversity of schools, theological traditions, and interpretive approaches within the Muslim world, all mainstream branches of Islam share the same essential creed. This is summarized in the Quranic declaration that this religion is one religion, and that God alone is to be worshipped, and given practical form in the well-known Prophetic teaching that Islam is built upon five pillars: bearing witness that there is no god but Allah and that Muhammad is His messenger (the shahada), establishing the five daily prayers, giving obligatory charity (zakat), fasting the month of Ramadan, and performing pilgrimage to Mecca (Hajj) for those able. Alongside these pillars, Sunni, Shia, and other mainstream traditions all affirm belief in one God, in His angels, in His revealed books, in all of His prophets culminating in Muhammad, and in the Day of Judgment. Differences among Muslims, over history's leadership dispute, schools of law, theological methodology, or spiritual emphasis, occur within this shared foundation rather than replacing it, which is why Muslims across these traditions recognize one another as fellow believers united in worshipping the same God through the same essential practices.
Q&A · Sects & Comparative Belief
What unites all Muslims despite these differences?
References
Sahih al-Bukhari 821:92
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.