Śatapatha Brāhmaṇa ("of a hundred paths") 2.2.1.20

2.2.1.20

tasyai virājau saṃyājye syātāmityāhuḥ | virāḍḍhīyamityatho triṣṭubhau triṣṭubbhīyamityatho jagatyau jagatī hīyamiti virājāvityeva syātām

For her, they say, the two samyâgyâs should be virâg verses; for the virâg is this (earth); or trishtubh verses, for the trishtubh is this (earth); or gagatî verses, for the gagatî is this (earth). Still, however, they should be virâg verses.