Xuansu was a native of Hejian, he claimed. He sold pills made from Croton tiglium seeds — a potent herb in Taoist medicinal tradition — in the city market, seven pills for one qian, claiming they could cure all kinds of illnesses. Prince Hejian was suffering from a tumor and bought the medicine; as a result, he expelled more than ten snakes. When asked about the meaning of the medicine, Su said: "The prince's tumor is a consequence of misfortune carried over from six generations — not something he himself has brought upon himself. The prince often releases young deer out of compassion for their mothers; his kind heart has moved heaven." An old retainer said: "My father has seen Su for generations, and Su has no shadow." The prince called Su to be examined at noon — indeed he had no shadow, a mark of true Taoist immortal attainment. The prince wanted to marry his daughter to him, but Su fled away during the night. Later people saw him beneath Changshan Mountain.

Substanceless and shadowless, at that time it was only Xuansu. The miraculous pills were entrusted to redeem the young deer. The Dao originated in Hejian, and at that time Xuansu was enjoying imperial favor. He soared like a dragon unbound by restraint, surpassing all others with his extraordinary talent.

The commentary says: The Yi Jing states that the Taiji gives rise to the Two Instruments — yin and yang. From the Two Instruments arise all things, and only then do people exist; with the existence of people comes birth and death. The meaning of life and death is thus clearly established. Indeed, all things in the world are spread out and formed as a whole, complete in every respect. How wondrous! How subtle! How refined! How minute! Sages looked upward to take the pattern from heaven, and downward to take the model from earth. The sun and moon move in their courses, the four seasons divide governance. Although heaven does not speak, its transformations cannot be said to be nonexistent. The Zhou Shu records that Sang Wen asked Juanzi: "If there is death, how can it also be said that immortals exist? Are these two matters both true?" Juanzi replied: "Such statements may indeed coexist." For instance, all grasses and trees sprout in spring and wither in autumn — this is certain — but among trees there are more than one hundred and eighty kinds such as pines and cypresses of the Five Sacred Mountains; among herbs there are zhiying, huangjing, and others that live on without dying. Even during severe winter, having endured frost and snow, they remain luxuriant and do not wither. Seeing such examples, what is there to find strange about the existence of Taoist immortals?