The Qur'an and Sunnah are the only two sources for the essential beliefs of those people who call themselves Muslims. What are those beliefs? The most important one is that there is no deity other than Allah. This is the first half of the attestation of every Muslim, the second half being that Muhammad is Allah's Prophet. There are a few other fundamental principles that a Muslim is required to accept, but further information is available elsewhere on this site. There is also information available on common misconceptions held by Muslims and non-Muslims.