Aitareya Āraṇyaka 1.3.1

1.3.1

hiṅkāreṇaitad ahaḥ pratipadyetety āhuḥ \
brahma vai hiṅkāro.
brahmaita/d ahar.
brahmaṇaiva tad brahma pratipadyate ya evaṃ veda \
yad eva hiṅkāreṇa pratipadyatā3i.
vṛṣā vai hiṅkāro, yoṣark.
tan mithunaṃ.
mithunam eva tad ukthamukhe karoti
prajātyai \
prajāyate prajayā paśubhir ya evaṃ veda \
yad v eva hiṅkāreṇa pratipadyatā3i.
yathā vā abhrir, evaṃ brahmaṇo hiṅkāro.
yad vai kiñcābhriyābhititṛtsaty, abhy evaitat tṛṇatty evam \
yaṃ kāmaṃ kāmayate, hiṅkāreṇābhy evainaṃ tṛṇatti ya evaṃ veda \
yad v eva hiṅkāreṇa pratipadyatā3i.
vāco vā eṣā vyāvṛttir daivyai ca mānuṣyai ca, yad dhi/ṅkāraḥ \
sa yad dhiṅkṛtya pratipadyate, vācam eva tad vyāvartayati daivīṃ ca mānuṣīṃ ca \\ 1 \\

Let him begin this day with singing 'Him,' thus they say.

Verily, the sound Him is Brahman, that day also is Brahman. He who knows this, obtains Brahman even by Brahman.

As he begins with the sound Him, surely that masculine sound of Him and the feminine Rik (the verse) make a couple. Thus he makes a couple at the beginning of the hymn in order to get offspring. He who knows this, gets cattle and offspring.

Or, as he begins with the sound Him, surely like a wooden spade, so the sound Him serves to dig up Brahman (the sap of the Veda). And as a man wishes to dig up any, even the hardest soil, with a spade, thus he digs up Brahman.

He who knows this digs up, by means of the sound Him, everything he may desire.

If he begins with the sound Him, that sound is the holding apart of divine and human speech.
Therefore, he who begins, after having uttered the sound Him, holds apart divine and human speech.