Śatapatha Brāhmaṇa ("of a hundred paths") 1.7.2.15

1.7.2.15

asau vā anavākyeyaṃ yājyā | sā vai gāyatrīyaṃ triṣṭubasau sa vai gāyatrīmanvāha tadamūmanubruvannasau hyanuvākyemāmanvāheyaṃ hi gāyatrī

The invitatory formula, doubtless, is yonder (sky), and the offering-formula is this (earth). The gâyatrî metre also is this (earth), and the trishtubh is yonder (sky) He recites the gâyatrî verse, thereby reciting yonder (sky), for the invitatory formula (anuvâkyâ) is yonder (sky). He recites this (earth), for the gâyatrî verse (viz. the offering-formula) is this (earth).