《庄子·外篇·刻意》
所以说，纯粹不混杂，宁静纯一不变不动。按自然规律来行动，这就是颐养心神的道理了。
故曰：纯粹而不杂，静一而不变，淡而无为，动而以天行，此养神之道也。
Therefore, it is said that pure and unmixed, calm and unmoving. Acting according to the laws of nature is the way to nourish the mind.