Jaiminīya (Talavakāra) Brāhmaṇa 1.127

1.127

yaduśanā kāvyo'paśyattasmādauśanamityākhyāyate
tatsvāraṃ bhavati
svareṇa vai devebhyo'ntato'nnādyaṃ pradīyate
ṛksamaṃ pavamānānte bhavati
narcā sāmātirecayanti narcaṃ sāmnā
tadyadiheva ceheva ca pavamane na stuvata etasyaiva samatāyai samaṃ kḷhaptyai
padānusvāraṃ purastādgāyatraṃ bhavati padānusvāramupariṣṭātpavamānānte
tasmādubhayataḥprāṇāḥ prajā ūrdhvāścāvācīśca
dviṣāmnī gāyatrī
yo'yamavāṅprāṇa eṣa eva saḥ
tasmādetena dvayaṃ prāṇena karoti bhasma ca karoti vātaṃ ca
dviṣāmnī bṛhatī
yo'yaṃ prāṅprāṇa eṣa eva saḥ
tasmādetena dvayaṃ prāṇena karoti retaśca siñcati mehati ca
ekasāmnī triṣṭup
nābhireva sā
tasyāmekaṃ sāma
tasmādetenaikameva prāṇena karoti yadeva prāṇānudanato'nūdaniti

Because Uśanā Kāvya saw it, therefore it is called the Auśana.
It has a final tone.
By means of the tone, food is given to the gods at the end.
At the end of the pavamāna, it equals the verse.
They do not make the sāman exceed the verse, nor the verse the sāman.
When they do not praise in the pavamāna here and here, it is for the sake of the equality of this, for proper arrangement.
Preceded by a tone with the verse-foot, the Gāyatra is in front; preceded by a tone with the verse-foot, it is above at the end of the pavamāna.
Therefore creatures have breaths on both sides, upward and downward.
The Gāyatrī has two sāmans.
It is this downward breath.
Therefore by this breath he performs two actions: he produces feces and he passes wind.
The Bṛhatī has two sāmans.
It is this forward breath.
Therefore by this breath he performs two actions: he discharges semen and he urinates.
The Triṣṭubh has one sāman.
It is the navel itself.
On it is one sāman.
Therefore with this single breath he performs only one action: whatever breath breathes out after breathing in.