There is a famous verse in the Upanishads that explicitly and specifically proclaims to hold the highest truth.
This verse was considered important enough that it was also incorporated into Shankara’s masterpiece Vivekachudamani and also Gaudapada‘s main work, his commentary on the Mandukya Upanishad (the Mandukya Karika).
In fact it is the only verse that I know of that is repeated not only in more than one Upanishad, but is also repeated by the two greatest traditional exponents of Advaita Vedanta (ie. Shankara and Gaudapada) in their subsequent works. Sri Ramana Maharshi also wrote a version of this verse.
Here is the verse:
‘There is neither destruction (Nirodha) nor creation (Utpatti), none in bondage (Bandha) and none practicing disciplines (Sadhaka). There is none seeking Liberation (Mumukshu) and none liberated (Mukta). This is the ultimate or highest truth (Paramartha).’
As I said above, this verse is found repeated in the Amritabindu Upanishad in verse 10, in the Atma Upanishad in verse 2.31. It was later incorporated by both Gaudapada (Mandukya Karika 2.32) and Shankara (Vivekachudamani verse 574) in their writings. Sri Ramana Maharshi also wrote a version of this verse himself which can be found as verse B28 in the text Guru Vachaka Kovai.
What do you think of this verse?