Shvetashvatara Upanishad 6.7-6.13
Let us know that highest great lord of lords, the highest deity of deities, the master of masters,
his high power is revealed as manifold, as inherent, acting as force and knowledge.
There is no master of his in the world, no ruler of his, not even a sign of him,
He is the cause, the lord of the lords of the organs, and there is of him neither parent nor lord.
He is the one God, hidden in all beings, all-pervading, the self within all beings,
watching over all works, dwelling in all beings, the witness, the perceiver, the only one, free from qualities.
The wise who perceive Him dwelling within their self,
to them belongs eternal happiness and serenity, not to others,
He who knows this God as primal cause,
through Sāṁkhya (reflection) and Yoga (self-discipline),
achieves Mukti (freedom).
~ Shvetashvatara Upanishad 6.7-6.13 Translated by Paul Deussen