The correct answer is:
The Quran is a sacred scripture and teachings that all Muslims follow. The primary-source scripture is the first pillar: profession of faith.
Explanation: The phrase "There is no god but Allah, and Muhammad is the Messenger of God" highlights the fundamental belief in the oneness of God and the prophethood of Muhammad, which constitutes the Shahada, the first pillar of Islam. The Quran serves as the central religious text of Islam, guiding the beliefs and practices of Muslims. The other options misrepresent the role of the Quran and the pillars of Islam.