The Savitri Upanishad (Sanskrit: सावित्री उपनिषत्), or Savitryupanishad, is a Sanskrit text and one of the minor Upanishads of Hinduism. It is attached to the Samaveda, and one of the Samanya Upanishads. The text title is related to the Hindu Sun god.
The Upanishad describes the Savitri-Vidya (knowledge of sunlight), asserting that everything in the universe is a manifestation of the masculine Savitr and feminine Savitri, elaborating on the Gayatri Mantra. The text also presents the Advaitic notion of nondual Brahman, as well as two mantras called the Bala (Strength) and Atibala (Super Strength) to meditate on Virat Purusha and Om.
The undivided, unidentified, unchanged and infinite energy of "Atibala" if not realized, then it shall be known in the name of "Bala" only. It means that undivided, unidentified, immutable energy, will be shown as changing from one form to another endlessly.
The mantra "Bala" saptham represents the 'Strength' and the mantra "Atibala" saptham represents the 'Extreme Strength'. He who synchronizes both the "Bala and Atibala" mantra sapthams in a perfect manner, through the saptham of "Bala" mantra overcomes death, and through the saptham of "Atibala" mantra attains immortality.
Ashtavakra Gita : Chapter-4
Rare is the man who knows himself as the undivided Lord of the world, and he who knows this is not afraid of anything.