The Ruyao Jing 入药镜 （The Mirror for Entering the Elixir）

Ruyao Jing (The Mirror for Entering the Elixir) was written by Cui Xifan of the Tang Dynasty. The Song Shi·Yiwen zhi (History of the Song Dynasty·Treatise on Arts and Literature) records Cui Gong Ruyao Jing (Master Cui’s Mirror for Entering the Elixir) in three volumes. Today, four versions survive in the Zhengtong Daozang (Orthodox Daoist Canon): Ruyao Jing Shangpian (First Chapter of The Mirror for Entering the Elixir) and Ruyao Jing Zhongpian (Middle Chapter of The Mirror for Entering the Elixir) included in volume 37 of Daoshu (Pivot of Dao); and Jiezhu Cui Gong Ruyao Jing (Annotated Explanation of Master Cui’s Mirror for Entering the Elixir) and Tianyuan Ruyao Jing (Celestial Origin Mirror for Entering the Elixir) included in volumes 13 and 21 of Xiuzhen Shishu (Ten Books on Cultivating Reality).

Ruyao Jing consists of eighty-two three-character verses. The entire text, in the form of pithy formulas, concisely expounds on alchemical methods. The term "ruyao" (entering the elixir) is a technical term in internal cultivation, referring to integrating one’s own essence, qi, and spirit with the creation and transformation of heaven and earth to refine a superior elixir, then guiding it into the dantian (cinnabar field). Through the refinement of "civil and martial fire phases," this becomes the inner elixir. "Jing" (mirror) here means "mirror/reflect"—the author recorded his cultivation methods for fellow practitioners to use as a reference and verification.

Ruyao Jing elaborates on the principles and methods of inner elixir cultivation, emphasizing the coordination of yin and yang qi within the human body. The author regards these as "nature and fate" (xingming) and metaphorically refers to them as water and fire, dragon and tiger, lead and mercury, etc., pointing out that the key lies in the application of "true intention" (zhenyi), also known as "Huangpo" (the Yellow Matriarch). The alchemical method described involves harmonizing yin and yang qi, making them converge to generate true yang qi, which serves as the medicine for the inner elixir (referred to as "lead from the water region"). This is then refined into an elixir using the "circulating heaven fire phases."

The text specifies that cultivating the inner elixir must imitate the creation and transformation of heaven and earth to attain "true water and true fire." It opposes blind exploration within oneself, advocating the coordination of the "nature and fate" of heaven and humans. It also repeatedly warns of the dangers in inner elixir cultivation, noting that even a minor mistake can lead to failure.

The alchemical ideas in Ruyao Jing have been valued by internal cultivation masters throughout history, becoming one of the classic works of Daoist inner alchemy and exerting a profound influence on later inner alchemy studies. As stated in Daoshu·Ruyao Jing Zhongpian: "Chunyangzi (note by the author: Lü Dongbin) once heard [these teachings] from Master Cui and sighed, ‘I now know that cultivation has a basis, that nature and fate are without error, and that the Dao is achieved therein.’" Lü Dongbin, having obtained Cui Xifan’s secret teachings on internal cultivation, once wrote a poem praising it: "After reading Master Cui’s Ruyao Jing, one’s mind becomes clear."

Famous Song Dynasty alchemists such as Liu Haichan, the Southern Song Daoist masters Zhang Boduan, Shi Tai, Bai Yuchan, and their disciples often quoted its theories, as did the Northern School. For example, Wang Daoyuan’s annotated version has been handed down, and Wu Shouyang elaborated on the profound meanings of this book in Tianxian Zhengli Zhilun (Direct Discourse on the Correct Principles of Heavenly Immortality). Moreover, the alchemical terms in Ruyao Jing were widely cited in Song and Yuan dynasty elixir texts.