In conducting research recently, I came across the writings of Hippocrates. Though he is miscredited with the precise phrase, "First, do no harm," he did write about abstaining from harming others -- medically or otherwise.
I really enjoyed a few, select lines from the contemporary version of the Hippocratic Oath, and thought you might, too:
I will remember that there is art to medicine as well as science, and that warmth, sympathy, and understanding may outweigh the surgeon's knife or the chemist's drug.
I will not be ashamed to say "I know not," nor will I fail to call in my colleagues when the skills of another are needed for a patient's recovery.
I will respect the privacy of my patients, for their problems are not disclosed to me that the world may know. Most especially must I tread with care in matters of life and death. If it is given me to save a life, all thanks. But it may also be within my power to take a life; this awesome responsibility must be faced with great humbleness and awareness of my own frailty. Above all, I must not play at God.
I will remember that I do not treat a fever chart, a cancerous growth, but a sick human being, whose illness may affect the person's family and economic stability. My responsibility includes these related problems, if I am to care adequately for the sick.
I will prevent disease whenever I can, for prevention is preferable to cure.
Adapted from the works of Hippocrates by Louis Lasagna, Academic Dean of the School of Medicine at Tufts University, 1964