Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.3.8

8.3.3.8

tāni vā etāni | trīṇi dvādaśānyupadadhāti tatṣaṭtriṃśatṣaṭtriṃśadakṣarā bṛhatyeṣā vai sā bṛhatī yāṃ taddevā antarikṣam bṛhatīṃ tṛtīyāṃ citimapaśyaṃstasyā etasyai devā uttamāḥ

These then are those (sets of) twelve he lays down,--that makes thirty-six, and the Brihatî consists of thirty-six syllables: this is that same Brihatî, the air, which the gods then saw as a third layer. In that (brihatî set of bricks) the gods come last (or, are highest).