Śatapatha Brāhmaṇa ("of a hundred paths") 7.1.2.17

7.1.2.17

ekaviṃśatirveva pariṣritaḥ | yajurdvāviṃśaṃ vyudūhanasya yajurūṣāśca yajuśca sikatāśca yajuśca purīṣaṃ ca yajuśca caturbhiḥ saṃnivapati vimuñcati pañcamena tatastribhiriyaṃ dvātriṃśadakṣarānuṣṭupsaiṣānuṣṭup

And, again, there are twenty-one enclosing-stones; the formula the twenty-second; the formula for the sweeping, the saline earth and its formula, the sand and its formula, the filling (soil) and its formula; with four (formulas) he pours (the two fires) together; with a fifth he unties (the pan); then this (Nirriti) with three,--the anushtubh verse consists of thirty-two syllables: this then is an anushtubh.