《伤寒论·辨太阳病脉证并治法上》
病在阳经的，大约七天可以痊愈；病在阴经的，大约六天可以痊愈。这是因为七属于阳数、六属于阴数的缘故。
发于阳者七日愈，发于阴者六日愈，以阳数七，阴数六故也。
The disease in the yang meridians can be cured in about seven days; the disease in the yin meridians can be cured in about six days. This is because seven belongs to the yang number, and six belongs to the yin number.