Among the Muslim Sufis, it is known as Sultan-ul-Azkar (the king of prayers). Another order of Sufiis call it Saut-i-Sarmadi, (the Divine Song). They also call it Kalam-i-qadim (the Ancient Sound), and the Kalma or "Word," Nida-e-Asmani (the Sound coming down from Heaven). The fourteen Tabaqs (regions) were made by the Kalma – the Word.
Khawaja Hafiz, a great divine, says:
From the turret of the Heaven, a call bids thee Home, But fallen into the snares thou listeneth not. No one knows where the Mansion of the Beloved lies, But sure enough, the chiming of the bells proceeds therefrom.
Take the stop-cock from thy ears, and hear thou the voice of emancipation coming to thee, Attach yourself not to the material world, The elixir of life is showering from above. The beat of Love while sounding in the Heavens, Sends blessings to the souls of the devotees.
Jalaluddin Rumi, in his Masnavi, says:
Grow not sceptical, but attune thyself to the Sound Coming down from the Heavens, Thy soul shall have revelations from afar. What are these? The glimpses of the Unrevealed; were I to speak of these sweet melodies, Even the dead shall rise from their graves.
Rise above the horizon, Oh brave soul, and hear the Melodious Song coming from the highest heaven.
Prophet Mohammed said that he heard the "Voice of God" as any other sound. Shah Niaz, another Muslim devotee, says:
Soul is the Will and the Secret of God. Its meditation is carried on without the help of tongue and palate. Alas! Thou art stuck fast in the physical bondage and do not hear the Holy Sound of God. My Beloved is speaking to thee all the while, but woe to thee for thou heareth not the Voice.
The whole universe is resounding with the Sound, and thou hast only to open the door of thine ears.
For opening the ears, it is sufficient to stop hearing the outer sounds. If you do this, you will hear the perpetual and unending Sound. It is infinite and has no beginning nor end, and on account of that, It is called Anhad (i.e., without any limits). Without this Word — the Eternal Sound — an expression of the Infinite, the world could not have come into existence. Hold communion with the Melodious Sound and lose yourself in it, Oh wise man.
Oh God! Show me that place from where the Kalma (Sound Principle) proceedeth without Words.
Source: ‘Naam or Word, Book I – Naam or Word, Evidence from various Religions: Islam’, by Kirpal Singh, 1894–1974.