“The silent and oral recitation (dikhr) of the “Affirmation of Unity” (La Illaha Il Allah), which is the root mantra at the foundation of Islam, is a core practice of all Sufis. The various orders can often be distinguished by the way that they do this.”
–Daniel Feldman, Qabalah: The Mystical Heritage of the Children of Abraham, 2001. Pg. 45.