Sāmānya

The Muktikā (Sanskrit: "deliverance") refers to the canon of 108 Upaniṣads. The date of composition of each is unknown, with the oldest probably from about 800 BCE and the youngest probably composed after the 15th-century CE. The Principal Upanishads were composed in the 1st millennium BCE, most Yoga Upanishads composed probably from the 100 BCE to 300 CE period, and seven of the Sannyasa Upanishads composed before the 3rd century CE.

The canon is part of a dialogue between Rama and Hanuman. Rama proposes to teach Vedanta, saying "Even by reading one verse of them [any Upanishad] with devotion, one gets the status of union with me, hard to get even by sages." Hanuman enquires about the different kinds of "liberation" (Mukti, hence the name of the Upanishad), to which Rama answers that "the only real type [of liberation] is Kaivalya".

The list of 108 Upanishads is introduced in verses 26-29:

But by what means is the Kaivalya kind of Moksha got? The Mandukya is enough; if knowledge is not got from it, then study the Ten Upanishads. Getting knowledge very soon, you will reach my abode. If certainty is not got even then, study the 32 Upanishads and stop. If desiring Moksha without the body, read the 108 Upanishads. Hear their order. (trans. Warrier)

Some scholars list ten as principal – the Mukhya Upanishads, while most consider twelve or thirteen as principal, most important Upanishads (highlighted).

The list of 108 names is given in verses 30-39. They are as follows:

Almost all printed editions of ancient Vedas and Upanishads depend on the late manuscripts that are hardly older than 500 years, not on the still-extant and superior oral tradition.Michael Witzel explains this oral tradition as follows:

The Vedic texts were orally composed and transmitted, without the use of script, in an unbroken line of transmission from teacher to student that was formalized early on. This ensured an impeccable textual transmission superior to the classical texts of other cultures; it is, in fact, something like a tape-recording.... Not just the actual words, but even the long-lost musical (tonal) accent (as in old Greek or in Japanese) has been preserved up to the present.

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Wikipedia