Shatapatha Brahmana 7.1.2.16

7.1.2.16

athātaḥ sampadeva | ekaviṃśatiriṣṭakā nava yajūṃṣi tattriṃśatsādanaṃ ca sūdadohāśca taddvātriṃtaddvātriṃśadakṣarānuṣṭupsaiṣānuṣṭup

Now then the (mystic) correspondence,--twenty-one bricks, nine formulas, that makes thirty;--and the 'settling' and Sûdadohas verse, that makes thirty-two,--the anushtubh verse consists of thirty-two syllables: this is an anushtubh.