Laghustavacarcastavau p28

p28

ātmaivedamagra āsīt puruṣavidhaḥ so'nuvīkṣya nānyadātmano'paśyat
so'hamasmītyagre vyāharattato'haṃnāmābhavat tasmādapyetarhi
āmantrito'hamayamityevāgre uktvāthānyannāma brūte ityādi . (bṛha0
1.4.1.17)

"In the beginning, this was indeed the Self alone, in the form of a person. Looking around, he saw nothing other than the Self. / He first uttered, 'I am He'; thence the name 'I' came to be. Therefore, even now, / when addressed, one first says 'This is I,' and then speaks whatever other name [he has]," and so forth (Bṛhadāraṇyaka Upaniṣad 1.4.1).