This is the clearest case in the collection of a formula that is genuinely and widely used and whose stated provenance does not survive checking.
It is chanted at the close of yoga classes across the English-speaking world, usually in a longer form ending with a triple invocation of peace, and it is routinely introduced as an ancient Sanskrit verse, a Vedic blessing, or a line from the Upanishads. No scholarly edition of the Rig Veda, of the principal Upanishads, or of the standard classical anthologies contains it. Searches of the digitised Sanskrit corpora do not produce it in a datable text. Attributions that circulate, to a specific Veda, to a named Upanishad, to a particular teacher, are given without a citation, and where a citation is offered it does not check out on inspection of the text named.
The Sanskrit itself is unremarkable and correct. It says: may all beings everywhere be happy and free. It resembles a large family of classical mangala verses, benedictions used to open or close a recitation, and there are genuinely old formulas of similar shape, including the well-attested wish that all be happy and free from illness. It is plausible that the couplet was assembled from that stock. It is not demonstrable.
Its actual currency is twentieth-century and transnational, spreading through modern postural yoga and the kirtan circuit, and it now appears on jewellery, studio walls and album titles.
None of this is an argument against reciting it. It is an argument for describing it accurately.