Shatapatha Brahmana 3.5.1.9

3.5.1.9

atha yatṣaṭtriṃśadvikramā prācī bhavati | ṣaṭtriṃśadakṣarā vai bṛhatī bṛhatyā vai devāḥ svargaṃ lokaṃ samāśnuvata tatho evaiṣa etadbṛhatyaiva svargaṃ lokaṃ samaśnute so 'sya divyāhavanīyo bhavati

Then as to why the 'easterly line ' is thirty-six steps long;--the Brihatî consists of thirty-six syllables, and by means of the Brihatî the gods obtained the heavenly world: and so does he now, by means of the Brihatî, obtain the heavenly world and that offering-fire (Âhavanîya) of his is in the sky.