素问·刺齐论 Treatise on the Correct Depths of Needling
黄帝问曰：愿闻刺浅深之分。歧伯对曰：刺骨者无伤筋，刺筋者无伤肉，刺肉者无伤脉，刺脉者无伤皮，刺皮者无伤肉，刺肉者无伤筋，刺筋者无伤骨。
帝曰：余未知其所谓，愿闻其解。歧伯曰：刺骨无伤筋者，针至筋而去，不及骨也。刺筋无伤肉者，至肉而去，不及筋也。刺肉无伤脉者，至脉而去，不及肉也。刺脉无伤皮者，至皮而去，不及脉也。所谓刺皮无伤肉者，病在皮中，针入皮中，无伤肉也。刺肉无伤筋者，过肉中筋也。刺筋无伤骨者，过筋中骨也。此之谓反也。
Huangdi asked: I wish to hear about the distinctions between shallow and deep needling. Qibo replied: When needling the bone, do not injure the sinews; when needling the sinews, do not injure the flesh; when needling the flesh, do not injure the vessels; when needling the vessels, do not injure the skin. Conversely, when needling the skin, do not injure the flesh; when needling the flesh, do not injure the sinews; when needling the sinews, do not injure the bone.
Huangdi said: I do not yet understand what this means; I wish to hear it explained. Qibo said: The fault of 'needling the bone yet injuring the sinews' means that the needle reaches only as far as the sinews and then withdraws, not reaching the bone. The fault of 'needling the sinews yet injuring the flesh' means the needle reaches only the flesh and withdraws, not reaching the sinews. The fault of 'needling the flesh yet injuring the vessels' means the needle reaches only the vessels and withdraws, not reaching the flesh. The fault of 'needling the vessels yet injuring the skin' means the needle reaches only the skin and withdraws, not reaching the vessels. As for what is called 'needling the skin yet injuring the flesh': the disease lies within the skin, but the needle, entering the skin, goes on to injure the flesh. 'Needling the flesh yet injuring the sinews' means the needle passes beyond the flesh into the sinews. 'Needling the sinews yet injuring the bone' means the needle passes beyond the sinews into the bone. This is what is meant by 'reversal,' the opposite of correct practice.