Shatapatha Brahmana 10.1.4.4

10.1.4.4

tṛtīyāṃ citiṃ cinoti sā hāsyaiṣā vyāna eva tadvai tadamṛtamamṛtaṃ hi vyānaḥ saiṣāmṛtacitistadetanmartyamubhayato'mṛtena parigṛhṇāti tenāsyaitadamṛtam bhavatyatha purīṣaṃ nivapati taddhāsyaitatsnāvaiva tadvai tanmartyaṃ hi snāva tadetasminnamṛte pratiṣṭhāpayati tenāsyaitadamṛtam bhavati

He lays down the third layer,--this, doubtless, is his through-breathing, and it is an immortal (element), for the through-breathing is something immortal: this, then, is an immortal layer. He thus encompasses that mortal (element) on both sides by an immortal one, and thereby that part of him becomes immortal. He then scatters loose soil thereon,--this, doubtless, is his sinews, and it is a mortal (element), for the sinew is mortal: he establishes it on that immortal (element), and thereby this part of him becomes immortal.