《太平广记·卷五十六·女仙一》
玄天老人说过，致虚到极点，守静到至诚，万物将自行恢复。
玄老有言，致虚极，守静笃，万物将自复。
The old man of Xuantian said, when one reaches the extreme of emptiness, and keeps quiet to the utmost sincerity, all things will restore themselves.