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"This self (atman) of mine that lies deep within my heart—"

Chandogya Upanishad
Chandogya Upanishad
The Chandogya Upanishad is a Sanskrit text embedded in the Chandogya Brahmana of the Sama Veda of Hinduism. It is one of the oldest Upanishads. In the Muktika canon of 108 Upanishads, it is listed as the ninth.
"This self (atman) of mine that lies deep within my heart—"
"So, those here in this world who depart without having discovered the self and these real desires"
"It is like this. Take a bird that is tied with a string. It will fly off in every direction and, when it cannot find a resting place anywhere else, it will alight back upon the very thing to which it is tied."