MĀṆḌŪKYA UPANISHAD · 1

ॐ इत्येतदक्षरमिदं सर्वं तस्योपव्याख्यानं
भूतं भवद् भविष्यदिति सर्वमोङ्कार एव
यच्चान्यत् त्रिकालातीतं तदप्योङ्कार एव ॥ १॥

oṃ ityetadakṣaramidaṃ sarvaṃ tasyopavyākhyānaṃ
bhūtaṃ bhavad bhaviṣyaditi sarvamoṅkāra eva
yaccānyat trikālātītaṃ tadapyoṅkāra eva ॥ 1॥

OM is this imperishable Word, OM is the Universe, and this is the exposition of OM. The past, the present and the future, all that was, all that is, all that will be, is OM. Likewise all else that may exist beyond the bounds of Time, that too is OM.

Sri Aurobindo · CWSA 18, p. 193