The Primordial Sound and the Mandukya Upanishad
The State of Pure Consciousness and Meditative Union
The Eternal Spark of the Divine
The Supreme, Infinite Reality of Vedanta
The Isha Upanishad, Yajurveda 40: eighteen mantras on seeing the Lord in all things, enjoying through renunciation, and joining knowledge with action.
The Mandukya Upanishad (Atharvaveda): twelve mantras on OM, the three states of consciousness and the silent fourth, Turiya.