Analects 15.24 is often cited as the "Reverse Golden Rule" and it's easy to see why:
Zigong asked: "Is there a single teaching that can be practiced to the end of one's life?" Confucius replied: "It is reciprocity! What you don't desire for yourself, do not desire for others."
The Golden Rule, "do unto others as you would have them do unto you," is found in the Gospels, in Matthew 7:9-12 and Luke 6:27-31. In the latter context, the "rule" follows a discussion of how one ought to treat one's enemies, while in the former, it is more general.
15.24 is interesting because it raises the question of just what status this "rule"–or better yet, "teaching" (for 言)–has among the many sorts of teachings found in the Analects. In some important ways, it rubs against the idea that for early Confucianism moral virtuosity is somehow incapable of codification, or somewhat stronger, incapable of adequate articulation. Is this a rule? a principle? an articulation of the Confucian dao by the author(s) of this passage? If not any of those, then what? Those who favor a virtue-emphasis reading of the Analects tend to focus on the term for reciprocity, shu 恕, and treat it as a virtue term, though the explanation in terms of the "rule" seems added to present something like a definitional equivalence. (Here, I'm thinking of Van Norden's discussion in "Unweaving the 'One Thread' of Analects 4:15″)
In 5.12, Zigong and Confucius have an exchange that is slightly different, on which Zigong comes off looking a bit too confident in himself:
Zigong said: "What I do not desire people to do to me, I also desire for it not to be done toward people." Confucius said, "Zigong my dear, it is not you who has gotten that far."
The phrasing, 一言, in 15.24 seems to indicate that there is something important, something on the order of a single principle, for which Zigong is asking. I wonder if there other, similarly explicit principles to be found in the Analects, if indeed 15.24 provides an explicit principle.