The Mishna (173b) taught a halakha presented by Rabban Shimon ben Gamliel in the interest of protecting the interests of the arev – individual who guaranteed payment – in the case of a ketuba. When a couple gets married, the marriage contract guarantees payment to the wife in the event of her husband’s death or divorce. If the ketuba payment was made by the arev rather than by the husband himself, Rabban Shimon ben Gamliel required the husband to take a vow that his ex-wife can no longer derive benefit from him. This was done in order to avoid the possibility that the couple would conspire to have the arev pay her so that they could then remarry.
In illustrating this ruling, the Gemara tells of a man named Moshe bar Atzari who had agreed to guarantee his daughter-in-law’s ketuba. His son, Rav Huna was in difficult financial straits, and Abaye raised the idea that he should divorce his wife, and after his father paid the ketuba he should remarry her. When Rava pointed out that he would be required to take the vow according to Rabban Shimon ben Gamliel’s ruling, Abaye argues that if they got divorced out of court, no one would require him to do so. In the end, it turned out that it was a family of kohanim, so it would have been impossible for him to divorce and remarry his wife.
The Gemara expresses shock at Abaye’s suggestion, given that Abaye is known to refer to someone who recommends such a course of action in a similar case (see above, daf 137b) as a rasha arum – an evil trickster. The Gemara responds that this case is unique because Rav Huna’s father certainly wanted to help out his son, especially since he was a scholar.
The Rashbam explains that he is a rasha (an evildoer) because he negates the wishes of the person who gave him the gift, and he is arum (a trickster) because he can successfully arrange for the gift to end up in the hands of another. He adds that Abaye only applies this appellation to someone who advises to do this. The person who does it, who is simply looking out for his own interests, would not be considered a rasha for doing this.