Nedarim, Chapter Four, Mishnah Four
The mishnah deals with several types of benefit that Shimon must refrain from giving Reuven who has sworn (or been sworn by Shimon) not to receive benefit from him.
1) If one is forbidden to benefit from his neighbor, and he pays him a visit [in sickness] he must stand, but not sit.
2) He may afford him a cure of life, but not a cure of money.
3) He may bathe together with him in a large bath, but not in a small one.
4) He may sleep in a bed with him.
a) Rabbi Judah said: in summer, but not in winter, because he thereby benefits him.
b) He may [nevertheless] recline with him on a couch.
5) [He may] eat at the same table with him but not out of the same bowl; but he may eat with him out of a bowl which returns.
a) He may not eat with him out of the food trough put before laborers.
6) He may not work with him on the same furrow, the words of Rabbi Meir.
a) But the Sages say: he may work at a distance from him.
Section one: Shimon may visit Reuven when he is sick, because that is a mitzvah. However, he shouldnt sit with him for a long time, because that would be causing benefit to Reuven.
Section two: The Talmud explains that Shimon may help cure Reuven for that is a commandment. However, he may not cure Reuvens animal for that is a monetary benefit.
Section three: If Shimon gets into a small bath with Reuven, he will raise the level of the bath water, and thereby benefit Reuven. Therefore he may not do so. However, he may get into a large bath with him where the water level will barely be raised.
Section four: He may sleep in bed with him, even though he warms up the bed. Rabbi Judah restricts this to the summer months, when it is warm anyway. However, even Rabbi Judah agrees that he may recline with him on the same couch, and we are not concerned lest he fall asleep.
Section five: Reuven may eat at the same table as Shimon, and we are not concerned lest Reuven eats from Shimons plate and thereby derives benefit. However, they may not eat out of the same communal bowl, lest Shimon intentionally leave the best part of the food for Reuven, and thereby cause him benefit. If the communal bowl was a returning bowl meaning one that was full of food, such that each person eating could eat his fill and still have leftovers, then they may share. In such a case, there is no concern that Shimon will leave food for Reuven because there is enough for everyone.
They may not eat out of the same bowl put before laborers, because laborers are always hungry and there are never leftovers. Therefore, Shimon might eat less so that Reuven could eat more.
Section six: According to Rabbi Meir they may not work plowing the same furrow, since if Shimon works harder he will benefit Reuven by allowing him to work less. The Sages allow them to work in the same furrow, as long as they keep their distance.