Śatapatha Brāhmaṇa ("of a hundred paths") 6.5.2.4

6.5.2.4

atha pūrvamuddhimādadhāti | rudrāstvā kṛṇvantu traiṣṭubhena candasāṅgirasvadityantarikṣaṃ haiṣa uddhistametadrudrāstraiṣṭubhena candasākurvaṃstathaivainamayametattraiṣṭubhena candasā karotyaṅgirasvaditi prāṇo vā aṅgirā dhruvāsīti sthirāsītyetadatho pratiṣṭhitāsītyantarikṣamasītyantarikṣaṃ hyeṣa uddhirdhārayā mayi prajāṃ rāyaspoṣaṃ gaupatyaṃ suvīryaṃ sajātānyajamānāyetyetadvai rudrā antarikṣaṃ kṛtvā tasminnetāmāśiṣamāśāsata tathaivaitadyajamāno 'ntarikṣaṃ kṛtvā tasminnetāmāśiṣamāśāste tāṃ saṃlipya saṃślakṣṇya

He then lays thereon the first (lower) side-part, with, 'May the Rudras, Aṅgiras-like, fashion thee by the Trishtubh metre!'--for this side-part is the air, and this the Rudras fashioned by means of the Trishtubh metre; and in like manner does this one now fashion it by means of the Trishtubh metre;--'Aṅgiras-like,' he says, for Aṅgiras is the breath;--'Thou art steadfast!'--that is, 'thou art firm,' or 'thou art fixed;'--'Thou art the air!' for this side-part is indeed the air;--'Establish in me offspring, increase of wealth, lordship of cattle, manhood, clansmen for the Sacrificer!' For the Rudras, having fashioned the air, invoked this blessing thereon; and in like manner does this Sacrificer, having fashioned the air, now invoke this blessing thereon. Having stroked and smoothed it all over--