Tao Te Ching · Ch. 14

視之不見,名曰夷;聽之不聞,名曰希;搏之不得,名曰微。此三者不可致詰,故混而為一。其上不皦,其下不昧。繩繩不可名,復歸於無物。是謂無狀之狀,無物之象,是謂惚恍。迎之不見其首,隨之不見其後。執古之道,以御今之有。能知古始,是謂道紀。

Shì zhī bù jiàn, míng yuē yí; Tīng zhī bù wén, míng yuē xī; Bó zhī bù dé, míng yuē wēi. Cǐ sān zhě bù kě zhì jié, gù hùn ér wéi yī. Qí shàng bù jiǎo, qí xià bù mèi. Shéng shéng bù kě míng, fù guī yú wú wù. Shì wèi wú zhuàng zhī zhuàng, wú wù zhī xiàng, shì wèi hū huǎng. Yíng zhī bù jiàn qí shǒu, suí zhī bù jiàn qí hòu. Zhí gǔ zhī dào, yǐ yù jīn zhī yǒu. Néng zhī gǔ shǐ, shì wèi dào jì.

Look at it and you cannot see it — its name is 'the invisible.' Listen to it and you cannot hear it — its name is 'the inaudible.' Reach for it and you cannot grasp it — its name is 'the impalpable.' These three cannot be further examined, so they merge and become one. Its top is not bright; its bottom is not dark. Unbroken, it cannot be named and returns to the state of no-thing. This is called the form of the formless, the image of no-thing — this is called the elusive and the vague. Meet it and you do not see its face; follow it and you do not see its back. Hold to the ancient Tao to govern present affairs. To know the ancient beginning — this is called the thread of Tao.

— Tao Te Ching 14

Source: Wang Bi edition (Chinese) + Hanyu Pinyin transliteration