Śatapatha Brāhmaṇa ("of a hundred paths") 6.3.1.44

6.3.1.44

yadveva caturbhiḥ | catasro vai diśaścatasṛṣu taddikṣu vācaṃ dadhāti tasmāccatasṛṣu dikṣu vāgvadati candobhiśca yajurbhiścādatte tadaṣṭau catasro diśaścatasro 'vāntaradiśaḥ sarvāsu taddikṣu vācaṃ dadhāti tasmātsarvāsu dikṣu vāgvadati

And, again, why with four (formulas);--there are four quarters: he thus lays speech into the four quarters, whence speech speaks in the four quarters. He takes it up both by metres and by formulas, that makes eight--there are four quarters, and four intermediate quarters: he thus lays speech into all the quarters, whence speech speaks in all the quarters.