वेदांतसारसंसिद्धं प्रणवार्थे प्रकाशनात् । एवमेव पुरा पृष्टो मंदरे नंदिकेश्वरः १६ ।
This has been explained in the meaning of the Praṇava (Om), the essence of Vedānta, by Nandikeśvara when asked by Sanatkumāra, the intelligent son of Brahmā, at the mountain Mandara.