[Advaita-l] Fwd: Looking for the source of a passage

[V Subrahmanian]

In the Brahma sutra bhashya 2.3.43, Shankara has cited a passage as from
the Atharva veda:

तथा ह्येके शाखिनो दाशकितवादिभावं ब्रह्मण आमनन्त्याथर्वणिका ब्रह्मसूक्ते — ‘
ब्रह्म दाशा ब्रह्म दासा ब्रह्मैवेमे कितवाः’ इत्यादिना ;

No editor has cited the source of the passage, as far as I could search.

Could anyone help locating the passage?

Thanks
subbu