PRAŚNA UPANISHAD · 4.1

अथ हैनं सौर्यायणि गार्ग्यः पप्रच्छ । भगवन्नेतस्मिन् पुरुषे
कानि स्वपन्ति कान्यस्मिञ्जाग्रति कतर एष देवः स्वप्नान् पश्यति
कस्यैतत् सुखं भवति कस्मिन्नु सर्वे सम्प्रतिष्ठिता भवन्तीति ॥ ४.१॥

atha hainaṃ sauryāyaṇi gārgyaḥ papraccha । bhagavannetasmin puruṣe
kāni svapanti kānyasmiñjāgrati katara eṣa devaḥ svapnān paśyati
kasyaitat sukhaṃ bhavati kasminnu sarve sampratiṣṭhitā bhavantīti ॥ 4.1॥

Then Gargya of the Solar race asked him, “Lord, what are they that slumber in this Existing and what that keep vigil? Who is this god who seeth dreams or whose is this felicity? Into whom do all they vanish?”

Sri Aurobindo · CWSA 18, p. 184