Aitareya Upanishad 2.1.5

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.

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:—