Brahma Knowledge, by L. D. Barnett, [1911], at sacred-texts.com

§ 10. Brahma is Absolute Being.—The question whether the universal substrate, or Brahma, should properly be called being (sat) or non-being (a-sat), already agitated the Vedic poets (see Ṛig veda, x. cxxix. 1), and passed through the schools of the Brāhmaṇas to those of the older Upanishads. The debate, however, was merely over words. As Brahma is beyond all the limiting conditions of phenomenal being, either term may be applied to it; it is at once metaphysically existent and empirically non-existent.

Brahma is non-being, B.A. II. iii. 1, Ch. III. xix. 1, Taitt. II. vi.-vii.; being, Ch. VI. ii. 1, etc. Brahma is "reality of reality," B.A. II. i. 20, iii. 6; "the Eternal cloaked in (empirical) reality," I. vi. 3. A reconciliation from the transcendental standpoint is found in Śvet. IV. 18, v. 1, Muṇḍ. II. ii. 1, etc. Śankara (on Brahma-sūtra, I. iv. 14 f.) rightly notes the twofold meaning of the terms "being" and "not-being."