The shahāda is the declaration by which one becomes a Muslim and the first pillar of Islam. Its first half, lā ilāha illā Allāh, is the most frequent formula of Sufi remembrance, read as a progressive negation of everything but God and affirmation of God alone.
Shahāda
The testimony of faith: there is no god but God, and Muhammad is the messenger of God.
Also: Shahada