कौषीतकि उपनिषद्

Kaushitaki Upanishad

The Kaushitaki Upanishad is an ancient Sanskrit text contained inside the Rigveda. It is associated with the Kaushitaki shakha, but a Sāmānya Upanishad, meaning that it is "common" to all schools of Vedanta. It was included in Robert Hume's list of 13 Principal Upanishads, and lists as number 25 in the Muktikā canon of 108 Upanishads.— Wikipedia