Shatapatha Brahmana 10.3.1.7

10.3.1.7

ya evāyam prajananaḥ prāṇaḥ eṣa triṣṭubiti tadya evaitasya prāṇasya mahimā yadvīryaṃ tadetatsahasrametasyaivaitatprāṇasya vīryaṃ yaddhyasya cinvata eṣa prāṇa ālubhyettata evaiṣo'gnirna cīyetaitenaivāsya rūpeṇa sahasrameṣa triṣṭubhaḥ saṃcito bhavati

'The Trishtubh is that generative (life-giving) breath,'--thus, whatever power, whatever vigour there is in that breath, that is this one thousand; and to that breath, indeed, this vigour belongs, for were that breath of him who builds it to become disordered, this fire-altar, assuredly, would not be built: by this its form that (altar) becomes built (so as to contain) a thousand Trishtubhs.