Śvetāśvatara Upaniṣad · 4..7

आत्मैवेदं सर्वम् तदन्यदपरं निरुक्तमवोचत् तद्वा एतद्विदित्वा योऽसावधोक्षजं विष्णुं महित्वे स्वर्गे पश्यति स सर्वेषु भूतेषु वसन्नेकी भवति

ātmaivedaṃ sarvam tadanyadaparaṃ niruktamavocat tadvā etadviditvā yo'sāvadhokṣajaṃ viṣṇuṃ mahitve svarge paśyati sa sarveṣu bhūteṣu vasannekī bhavati

The Ātman is all this. That is the other, the distant —thus declared Nirukta. Knowing this, he who sees Viṣṇu, the Adhokṣaja, in the greatness of heaven, he dwells in all beings, becomes one.

Repetition of the previous verse with the crucial addition: ekī bhavati —“becomes one.” It is not that one sees unity from outside, but identifies with it. In our yoga practice, this is the consummation of sādhana: not contemplating unity as object but being unity itself. He who dwells in all beings does not dwell in them as visitor but as their own being. To be ekī (one) is not solitary but total inclusion of multiplicity in non-dual unity.