Śatapatha Brāhmaṇa ("of a hundred paths") 10.2.3.4

10.2.3.4

sa vedyantāt ṣaṭtriṃśatprakramām prācīṃ vediṃ vimimīte triṃśatam paścāttiraścīṃ caturviṃśatim purastāttannavatiḥ saiṣā navatiprakramā vedistasyāṃ saptavidhamagniṃ vidadhāti

From the (western) end of the Vedi he measures off the Vedi thirty-six steps long eastward, thirty (steps) broad behind, and twenty-four (steps broad) in front,--that makes ninety. This, then, is the Vedi measuring ninety steps: thereon he lays out the sevenfold Fire-altar.