The Silver Rule, "Do not do unto others what you would not have them do unto you", is a standard of behaviour found in the writings of, amongst others, Hillel the Elder. Carl Sagan refers to it as the converse of the ethical principle of the Golden Rule.
The Silver Rule is similar in meaning to the Hippocratic Oath, known best for the declaration "do no harm". Hippocrates wrote, in his Epidemics, Bk. I, Sect. XI. "Declare the past, diagnose the present, foretell the future; practice these acts. As to diseases, make a habit of two things — to help, or at least to do no harm." The shorter expression might be interpreted as a simplification of the longer one.