The shahada (Arabic: الشهادة‎ aš-šahādah  audio (help·info)) (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:

In Shia Islam, the creed is expanded with the addition of a phrase concerning Ali at the end:

The word shahādah is a noun stemming from the verb shahida, meaning “to observe, witness, or testify”; 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 (= "two testifyings"), which refers to dual act of observing or seeing and then the declaration of the observation. 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, shahādah can mean “martyrdom”, the shahid (“martyr”) demonstrating the ultimate expression of faith.

Yusuf Estes (born in 1944) is an American Muslim preacher and teacher who converted from Christianity to Islam in 1991. He was a Muslim Chaplain for the United States Bureau of Prisons through the 1990s. He was a Muslim Delegate to the United Nations World Peace Conference for Religious Leaders held at the U.N. in September 2000.

Active in Islamic missionary work in the United States, Estes is often featured as guest presenter and keynote speaker at various Islamic events as well as frequently appearing on various Islamic satellite TV channels. Estes takes a dim view of today's public school system in the United States for any children, and highly recommends schools where they might receive a religious education combined with more advanced scholastic education.

Yusuf Estes was born in Ohio, and was raised in Houston, Texas in a Anglo-Saxon Protestant family. From 1962 to 1990, his career was in the music, entertainment and marketing fields. He also taught music and served as a music minister. He owned several musical instrument companies including the Estes Piano and Organ Company. He produced and directed live entertainment programs in the United States from the mid 1960s until his last endeavor for cable TV in Florida, entitled 'Estes Music Jamboree'.

Hamza Yusuf Hanson is an American Islamic scholar, and (with Zaid Shakir and Hatem Bazian) is co-founder of Zaytuna College in Berkeley, California, United States. He is a convert to Islam, and is one of the signatories of A Common Word Between Us and You, an open letter by Islamic scholars to Christian leaders, calling for peace and understanding. He has described the 9/11 attacks as "an act of 'mass murder, pure and simple'". Condemning the attacks, he has also stated "Islam was hijacked ... on that plane as an innocent victim".The Guardian newspaper in the United Kingdom reported that he "is arguably the west's most influential Islamic scholar" and added that "many Muslims find his views hard to stomach."

Hamza Yusuf was born to two academics in Washington State and raised in Northern California. In 1977, he became Muslim and subsequently traveled to the Muslim world and studied for ten years in the United Arab Emirates, Saudi Arabia, as well as North and West Africa. Hamza Yusuf spent four years studying in the United Arab Emirates and elsewhere in the Middle East. Later he traveled to West Africa and studied in Mauritania, Medina, Algeria, and Morocco under such scholars as Murabit al Haaj; Baya bin Salik, head of the Islamic court in Al-'Ain, United Arab Emirates; Muhammad Shaybani, Mufti of Abu Dhabi; Hamad al-Wali; and Muhammad al-Fatrati of Al Azhar University in Cairo, Egypt.^{[citation needed]} After more than a decade abroad, he returned to the United States and earned degrees in nursing from Imperial Valley College and religious studies at San José State University.^{[citation needed]}

Shaykh Ahmad ibn Zayn al-Dín ibn Ibráhím al-Ahsá'í (Arabic: شيخ أحمد بن زين الدين بن إبراهيم الأحسائي‎) was (1753–1826) was the founder of a 19th century Shi`i school in the Persian and Ottoman empires, whose followers are known as Shaykhís.

He was a native of the Al-Ahsa region (Eastern Arabian Peninsula), educated in Bahrain and the theological centers of Najaf and Karbala in Iraq. Spending the last twenty years of his life in Iran, he received the protection and patronage of princes of the Qajar dynasty.

Little is documented about the early life of Shaykh Ahmad, except that he was born in Ahsa, in the northeast of the Arabian peninsula, to a Shi'i family of Sunni origin in either the year 1166 A.H. (1753 C.E.), or 1157 A.H. (1744 C.E.). Nabíl-i-A`zam, a Baha'i historian, documents his spiritual awakening in his book The Dawn-Breakers as follows:

While it is unclear how much of Nabil's interpretation is consistent with Shaykh Ahmad's true feelings, the underlying motivations for reform, and ultimately for messianic expectation, become somewhat clearer.