अत्र प्रमाणं वेदान्ता गुरवोऽनुभवस्तथा ।ब्रह्मैवाहं न संसारी न चाहं ब्रह्मणः पृथक् ॥ २७ ॥
In plain words
The authority here is threefold: the Upaniṣads, the teachers, and your own direct experience. I am Brahman itself — not someone caught turning in saṃsāra, and not anything standing apart from Brahman.
Close to the Sanskrit
Here the authority is the Vedāntas, the teachers, and likewise direct experience. Brahman alone am I; not a transmigrator; nor am I separate from Brahman.