Aitareyabrahmana 2.21

2.21

śiro vā etad yajñasya yat prātaranuvākaḥ, prāṇāpānā upāṃśvantaryāmau,
vajra eva vāṅ. nāhutayor upāṃśvantaryāmayor hotā vācaṃ visṛjeta
yad ahutayor upāṃśvantaryāmayor hotā vācaṃ visṛjeta,
vācā vajreṇa yajamānasya prāṇān vīyāḍ ya enaṃ tatra brūyād:
vācā vajreṇa yajamānasya prāṇān vyagāt, prāṇa enaṃ hāsyatīti,
śaśvat tathā syāṭ tasmān nāhutayor upāṃśvantaryāmayor hotā vācaṃ visṛjeta
prāṇaṃ yacha svāhā tvā suhava sūryāyety upāṃśum anumantrayeta,
tam abhiprānet: prāṇa prāṇam me yachety.
āpanāṃ yacha svāhā tvā suhava sūryāyety antaryāmam anumantrayeta,
tam abhyapāned: apānāpānam me yacheti.
vyānāya tvety upāṃśusavanaṃ grāvāṇam abhimṛśya vācaṃ visṛjata
ātmā vā upāṃśusavana,
ātmany eva tad dhotā prāṇān pratidhāya vācaṃ visṛjate sarvāyuḥ sarvāyutvāya
sarvam āyur eti ya evaṃ veda

ii. 21 (viii. 3). The morning litany is the head of the sacrifice; the Upāṅçu and Antaryāma (cups) are expiration and inspiration; speech verily is a thunderbolt. Before the Upāṅçu and Antaryāma (cups) have been offered the Hotṛ should not utter speech; if, before the Upāṅçu and the Antaryāma (cups) have been offered, the Hotṛ should utter speech, with speech as a thunderbolt he would interrupt the breaths of the sacrificer. If one were to say then of him, ‘With speech as a thunderbolt he has interrupted the breaths of the sacrificer, breath will forsake him,’ it would assuredly be so. Therefore the Hotṛ should not utter speech before the Upāṅçu and Antaryāma (cups) have been offered. With ‘Support expiration; hail! thee, O easy to invoke, to the sun!’ he should accompany the Upāṅçu (cup) ; towards it he should breath forth with ‘O expiration, support my expiration.’ With ‘Support inspiration; hail! thee, O easy to invoke, to the sun!’ he should accompany the Antaryāma (cup); towards it he should breath in with ‘O inspiration, support my inspiration’; ‘To cross-breathing thee!’ with this he utters speech, having touched the stone for pressing (the Soma for) the Upāṅçu. Verily thus the Hotṛ, having placed the breaths in the body, utters speech, with the whole of life, for the whole of life; a full life he lives who knows thus.