Śvetāśvatara Upaniṣad · 6..4
तद् वै तत् सत्यं सत्यं वै तत् सत्यस्य सत्यं तद् वै तत् सत्यं सत्यं वै तत्
tad vai tat satyaṃ satyaṃ vai tat satyasya satyaṃ tad vai tat satyaṃ satyaṃ vai tat
That in truth is the Truth. The Truth in truth is That. The Truth of truth —that in truth is the Truth. The Truth in truth is That.
Repetition of the previous verse, intensifying the liturgy of Truth. In our yoga practice, this repetition is meditation: each affirmation is an opportunity to immerse more deeply in the understanding that there is only One Reality. Satyasya satyaṃ —the Truth of truth— is what remains when all relative truths have been transcended. It is not negation of the world but recognition of its foundation. That (tat) is the basis, not the based.