Śatapatha Brāhmaṇa ("of a hundred paths") 1.8.2.12

1.8.2.12

atha narāśaṃsaṃ dvitīyaṃ yajati | antarikṣaṃ vai narāśaṃsaḥ prajā vai narastā imā antarikṣamanu vāvadyamānāḥ prajāścaranti yadvai vadati śaṃsatīti vai tadāhustasmādantarikṣaṃ narāśaṃso 'ntarikṣamu vai triṣṭuptattriṣṭubhaṃ dvitīyāmakurvan

In the second place he offers to Narâsamsa. Now, Narâsamsa is the air. Man (nara), namely, means (human) being; and these same beings move about in the air speaking aloud. And when he (man) speaks, they say 'he chants (sams);' and therefore Narâsamsa is the air. But the trishtubh also is the air, and for this reason they have placed the trishtubh second.