Subala Upanishad of Shukla-yajurveda, Chapter III

"At first, there was Asat, unborn, non-existent, unsupported, soundless, touchless, formless, tasteless, odourless, and decayless. The undaunted man never grieves, as he knows Ātmā to be great, all-pervading and unborn. It (Ātma) is prāṇaless, mouthless, earless, tongueless, manas-less, tejas-less, eyeless, nameless, gotraless (or clanless), headless, handless, feetless, non-unctuous, bloodless, non-measurable, neither long nor short, neither gross nor atomic, neither great nor small, endless, indescribable, nonreturnable, non-luminous, not hidden, having neither inside nor outside, neither eating anything nor being eaten by others. Some one (out of many) attains to this (Ātmā) by the six means of satya (truth), dāna (charity), tapas (religious austerities), non-injury to any creature, celibacy and complete indifference to worldy objects; ^[1] and there are no other means. Whoever feels happy with the thought 'I know That', that learned person's prāṇa will never get out of his body at the moment of death, but will become absorbed in Brahman; and being absorbed in Brahman, he attains the state of Brahman Itself as he who knows this."