(Beraisa): If a person transgressed and had business dealings with an idolater within three days of their festival, he may benefit from the money.

(R. Yaakov bar Acha/ R. Yosi citing R. Yochanan): This applies even if he did this on the actual day of the festival.

Support (Beraisa): When is there the three day prohibition? When the idolater does not know the Jew (and he might think that the Jew is doing business because he holds the idolater in high regard); but if he knows him, it is permitted even on the day of the festival, as the idolater knows that it is not because the Jew holds him in high regard, but rather, the Jew does not want to lose this opportunity to earn some money.

(Beraisa): If a person entered a city and found idolaters celebrating their festival, he may rejoice with them, as it could otherwise cause hatred.

A Roman captain once honored R. Yehuda HaNasi (the grandson of Rebbi) by giving him a sack of gold dinars on the day of their festival. R. Yehuda returned to him the whole sack as he did not need it, but he kept one dinar in order to prevent hatred.

He asked R. Shimon ben Lakish about the coin who told him to throw its value into the Yam HaMelach (Dead Sea).

Question: This was a case where the idolater knew him and he had already received it, so why did R. Shimon ben Lakish tell him to throw away its value?

(R. Abahu): As for me, Rabban Gamliel b'Rebbi asked me if it is permitted to go to a fair that is made in honor of an idol, and I prohibited him to go.

Question (Beraisa): One may go to a fair and buy male and female slaves...?

(Reish Lakish): Not only is it permitted to buy a Jewish slave back from an idolater but it is even permitted to buy a gentile slave from the fair, in order to bring him to the way of Hash-m.

Question: So why did Reish Lakish prohibit R. Yehuda HaNasi from benefiting from the money?

Answer: Rabban Gamliel wasn't yet a great Rabbi and R. Abahu wanted to teach him not to become accustomed to doing business with the idolaters on their festival.

Question: But why did Reish Lakish rule that R. Yehuda HaNasi should not benefit, if he was already a great Rabbi?

Answer: Reish Lakish prohibited it for the sake of the onlookers.