Aitareya Upaniṣad 2.1

2.1.1

puruṣe ha vā ayam ādito garbho bhavati yad etad retaḥ.
tad etat sarvebhyo 'ṅgebhyas tejaḥ sambhūtam ātmany evātmānaṃ bibharti.
tad yadā striyāṃ siñcaty athainaj janayati.
tad asya prathamaṃ janma.

1. In a person (_puruṣa_), verily, this one becomes at first an embryo (_garbha_). That which is semen (_retas_), is the vigor (_tejas_) come together from all the limbs. In the self, indeed, one bears a self. When he pours this in a woman, then he begets it. This is one's first birth.

2.1.2

tat striyā ātmabhūyaṃ gacchati yathā svam aṅgaṃ tathā.
tasmād enāṃ na hinasti.
sāsyaitam ātmānam atra gataṃ bhāvayati.

2. It comes into self-becoming (_ātma-bhūya_) with the woman,

just as a limb of her own. Therefore it injures her not. She nourishes this self of his that has come to her.

2.1.3

sā bhāvayitrī bhāvayitavyā bhavati.
taṃ strī garbhaṃ bibharti.
so 'gra eva kumāraṃ janmano 'gre 'dhi bhāvayati.
sa yat kumāraṃ janmano 'gre 'dhi bhāvayaty ātmānam eva tad bhāvayaty eṣāṃ lokānāṃ santatyai.
evaṃ santatā hīme lokāḥ.
tad asya dvitīyaṃ janma.

3. She, being a nourisher, should be nourished. The woman bears him as an embryo. In the beginning, indeed, he nourishes the child [and] from birth onward. While he nourishes the child from birth onward, he thus nourishes his own self, for the continuation of these worlds; for thus are these worlds continued. This is one's second birth.

2.1.4

so 'syāyam ātmā puṇyebhyaḥ karmebhyaḥ pratidhīyate.
athāsyāyam itara ātmā kṛtakṛtyo vayogataḥ praiti.
sa itaḥ prayann eva punar jāyate.
tad asya tṛtīyaṃ janma.

4. This self of one is put in one's place for pious deeds (puṇya karman). Then this other self of one, having done his work (kṛta-kṛtya), having reached his age, deceases. So, deceasing hence indeed, he is born again. This is one's third birth. As to this it has been said by a seer:—

2.1.5

tad uktam ṛṣiṇā.
garbhe nu sann anv eṣām avedam ahaṃ devānāṃ janimāni viśvā.
śataṃ mā pura āyasīr arakṣann adha śyeno javasā nir adīyam.
iti.
garbha evaitac chayāno vāmadeva evam uvāca.

5. Being yet in embryo, I knew well All the births of these gods!

A hundred iron citadels confined me, And yet, a hawk (śyena) with swiftness, forth I flew!

In embryo indeed thus lying (śayāna), Vāmadeva spoke in this wise.

2.1.6

sa evaṃ vidvān asmāc charīrabhedād ūrdhvam utkramyāmuṣmin svarge loke sarvān kāmān āptvāmṛtaḥ samabhavat samabhavat.

6. So he, knowing this, having ascended aloft from this separation from the body (śarīra-bheda), obtained all desires in the heavenly world (svarga loka), and became immortal—yea, became [immortal]!