Shahadah

The shahada (Arabic: الشهادة‎ aš-šahādah) (from the verb شهد šahida, "he witnessed"), means "to know and believe without suspicion, as if witnessed, testification"; it is the name of the Islamic creed. The shahada is the Muslim declaration of belief in the oneness of God (tawhid) and acceptance of Muhammad as God's prophet. The declaration in its shortest form reads:

لَا إِلَّهَ إِلَّا الله مُحَمَّدٌ رَسُولُ الله (lā ʾilāha ʾillā l-Lāh, Muḥammadun rasūlu l-Lāh) (in Arabic)

There is no god but God, Muhammad is the messenger of God. (in English)

In Shia Islam, the creed is expanded with the addition of a phrase concerning Ali at the end, although not obligatory:

وعليٌ وليُّ الله (wa ʿAliyyun waliyyu l-Lāh) ["and Ali is the wali (friend; viceregent) of God"].
The word shahādah (شِهادة) is a noun stemming from the verb shahada (شَهَدَ) , meaning "he observed, witnessed, or testified"; when used in legal terms, shahādah is a testimony to the occurrence of events, such as debt, adultery, or divorce. The shahādah can also be expressed in the dual form shahādatān (شِهادَتانْ, lit. "two testimonials"), which refers to the dual act of observing or seeing and then the declaration of the observation.The person giving the testimony is called a shāhid (شاهِد), with the stress on the first syllable. The two acts in Islam are observing or perceiving that there is no god but God and testifying or witnessing that Muhammad is the messenger of God. In a third meaning, shihādah or more commonly istishhād (إسْتِشْهادْ), means "martyrdom", the shahīd (شَهيد) pronounced with stress on the last syllable ("martyr") demonstrating the ultimate expression of faith. Shahīd can also be used in a non-Islamicreligious context. Long before the advent of Islam, Christian Arabs of the Middle East used the word shahīd referencing to someone that was wrongly killed or someone that died for his family, his Christian faith or his country. The two words shāhid (شاهِد, "witness") and shahīd (شَهيد, "martyr") are pre-Islamic. Both are paradigms of the root verb (شَهَدَ, shahada, "he observed").
A single honest recitation of the shahādah in Arabic is all that is required for a person to become a Muslim. This declaration, or statement of faith, is called the kalimah (كَلِمة, lit. "word"). Recitation of the shihādah, the "oath" or "testimony", is the most important article of faith for Muslims. Non-Muslims wishing to convert to Islam do so by a public recitation of this creed. Sunni Muslims count it as the first of the Five Pillars of Islam, while the Twelver and Ismaili Shi'a connect it to their respective lists of pillars of the faith. The complete shahādah cannot be found in the Quran, but comes from hadiths.