All things whatsoever ye would that men should do to you, do ye so to them; for this is the law and the prophets.
Do not do to others what you would not like yourself. Then there will be no resentment against you, either in the family or in the state.
Hurt not others in ways that you yourself would find hurtful.
This is the sum of duty; do naught onto others what you would not have them do unto you.
No one of you is a believer until he desires for his brother that which he desires for himself.
What is hateful to you, do not do to your fellowman. This is the entire Law; all the rest is commentary.
Talmud, Shabbat 3id
Regard your neighbor’s gain as your gain, and your neighbor’s loss as your own loss.
Tai Shang Kan Yin P’ien
That nature alone is good which refrains from doing another whatsoever is not good for itself.
Adapted from "The Christopher Newsletter"