Terminology and significance
In the English translation—"There is no god but God. Muhammad is the messenger of God."—the first, lower-case occurrence of "god" is a translation of the Arabic word ilah, while the capitalized second and third occurrence of "God" are translations of the Arabic word Allah.
The noun šahāda (شَهادة), from the verbal root šahida ([ˈʃahɪd(a)] شَهِدَ) meaning "to observe, witness, testify", translates as "testimony" in both the everyday and the legal senses.[note 2] The Islamic creed is also called, in the dual form, šahādatān (شَهادَتانْ, literally "two testimonials"). The expression al-šahāda (the Witnessed) is used in Quran as one of the "titles of God".
In Sunni Islam, the Shahada has two parts: la ilaha illa'llah (None has the right to be worshipped except God), and Muhammadun rasul Allah (Muhammad is the messenger of God), which are sometimes referred to as the first Shahada and the second Shahada. The first statement of the Shahada is also known as the tahlīl.
In Shia Islam, the Shahada also has a third part, a phrase concerning Ali, the first Shia Imam and the fourth Rashid caliph of Sunni Islam: وعليٌ وليُّ الله (wa ʿalīyyun walīyyu-llāh [wa ʕaˈlɪj.jʊn waˈlɪj.jʊlˈɫɑː]), which translates to "Ali is the wali of God".
In the Quran, the first statement of the Shahadah takes the form la ilaha illa'llah twice (37:35, 47:19), and allahu la ilaha illa hu (God, None has the right to be worshipped but He) much more often. It appears in the shorter form la ilaha illa Hu (None has the right to be worshipped except He) in many places. It appears in these forms about 30 times in the Quran, and never attached with the other parts of the Shahadah in Sunni or Shia Islam or "in conjunction with another name".
Islam's monotheistic nature is reflected in the first sentence of the Shahada, which declares belief in the oneness of God and that he is the only entity truly worthy of worship. The second sentence of the Shahada indicates the means by which God has offered guidance to human beings. The verse reminds Muslims that they accept not only the prophecy of Muhammad but also the long line of prophets who preceded him. While the first part is seen as a cosmic truth, the second is specific to Islam, as it is understood that members of the older Abrahamic religions do not view Muhammad as one of their prophets.
The Shahada is a statement of both ritual and worship. In a well-known hadith, Muhammad defines Islam as witnessing that there is no god but God and that Muhammad is God's messenger, giving of alms (zakat), performing the ritual prayer, fasting during the month of Ramadan and making a pilgrimage to the Kaaba: the five pillars of Islam are inherent in this declaration of faith.