Aitareya Āraṇyaka 2.3.8

2.3.8

a iti brahma.
tatrāgatam aham iti \
tad vā idaṃ bṛhatīsahasraṃ saṃpannaṃ.
tasya vā etasya bṛhatīsahasrasya saṃpannasya ṣaṭtriṃśatam akṣa/rāṇāṃ sahasrāṇi bhavanti.
tāvanti puruṣāyuṣo 'hnāṃ sahasrāṇi bhavanti \
jīvākṣareṇaiva jīvāhar āpnoti, jīvāhnā jīvākṣara/m iti \
anakāmamāro 'tha devarathas.
tasya vāg uddhiḥ, śrotre pakṣasī, cakṣuṣī yukte, manaḥ saṃgrahītā.
tad ayaṃ prāṇo 'dhitiṣṭhati \
tad uktam ṛ/ṣiṇā \
ā tena yātaṃ manaso javīyasā (RV X 39,12a), nimiṣaś cij javīyasā- (RV VIII 73,2a) -iti, javīyaseti \\ 8 \\
\\ ity aitareyadvitīyāraṇyake tṛtīyo 'dhyāyaḥ \\

Brahman (as hidden beneath prâna) is called the A; and the I (ego) is gone there (the worshipper should know that he is uktha and prâna).

This becomes perfect as a thousand of Brihatî verses, and of that hymn, perfect with a thousand Brihad verses, there are 36,000 syllables. So many are also the thousands of days of human life. By means of the syllable of life (the a) alone (which is contained in that thousand of hymns) does a man obtain the day of life (the mahâvrata day, which completes the number of the days in the Gavâmayana, sacrifice), and by means of the day of life (he obtains) the syllable of life.

Now there is a chariot of the god (prâna) destroying all desires (for the worlds of Indra, the moon, the earth, all of which lie below the place of Hiranyagarbha). Its front part (the point of the two shafts of the carriage where the yoke is fastened) is speech, its wheels the cars, the horses the eyes, the driver the mind. Prâna (breath) mounts that chariot (and on it, i. e. by means of meditating on Prâna, he reaches Hiranyagarbha).

This has been said by a Rishi (Rv. X, 39, 12):--

'Come hither on that which is quicker than mind,' and (Rv. VIII, 73, 2) 'Come hither on that which is quicker than the twinkling of an eye,' yea, the twinkling of an eye.