Bhagavad Gita · Chapter 13: The Field and the Knower of the Field
Bhagavad Gita 13.12
ज्ञेयं यत्तत्प्रवक्ष्यामि यज्ज्ञात्वामृतमश्नुते ।
अनादिमत्परं ब्रह्म न सत्तन्नासदुच्यते ॥
jñeyaṃ yattatpravakṣyāmi yajjñātvāmṛtamaśnute | anādimatparaṃ brahma na sattannāsaducyate ||
I will now describe what is to be known, by knowing which one attains immortality: the supreme Brahman, which has no beginning, and which is said to be neither being nor non-being.
Modern context
Now Krishna turns to what is to be known: Brahman, without beginning, which is said to be neither being nor non-being. This is not a riddle for its own sake. Everything we normally call 'being' is a thing among things. Everything we call 'non-being' is the absence of a thing. The ground of all things is neither. It cannot be placed in either category, because both categories arise within it.