Prose
[ब्रा. ३.
In plain words
This is a page marker, not a passage of Śaṅkara's text: a stray fragment of the printed edition's running header ('[Brāhmaṇa 3.'), not Sanskrit prose to be translated.
Close to the Sanskrit
This record is not Sanskrit prose. It is a fragment of a printed running page-header — '[Brāhmaṇa 3.' — a cross-reference marker that slipped into the source scan, broken off before its continuation.