Gittin 30B

איכא בינייהו עניי כותיים.

The Talmud answers: There is a difference between them where the only poor people to be found are poor Samaritans. According to R' Eliezer ben Ya’akov, they are not considered to be converts (see Kiddushin 75b), and one may not continue the arrangement with them serving as the poor people. According to R' Aḥai, they are considered converts, and one may continue the arrangement with them serving as the poor people.

העשיר העני ⁠– אין מפריש עליו, וזכה הלה במה שבידו.

It was taught in a baraita (Tosefta 3:1) that if the poor person became wealthy then the homeowner may no longer separate tithes based on his outstanding loan, and the borrower, who is now wealthy, acquires the money remaining in his possession. This is because from the outset the understanding was that the loan would be repaid only by separating the poor man’s tithe.

ורבנן, מאי שנא למיתה דעבוד תקנתא, ומאי שנא לעשירות דלא עבוד תקנתא? מיתה שכיחא, עשירות לא שכיחא. אמר רב פפא, היינו דאמרי אינשי: חברך מית ⁠– אשר, איתעשר ⁠– לא תאשר.

The Talmud asks: And according to the rabbis, what is different about death, when the poor man dies, that they instituted an ordinance to enable the homeowner to continue to separate tithes based on other poor people, and what is different about wealth, when the poor man becomes wealthy, that they did not institute an ordinance? The Talmud answers: Death is common, whereas wealth is not common, and the rabbis did not enact an ordinance for an uncommon circumstance. Rav Pappa said: This explains the folk saying that people say: If one says to you that your friend died, then believe it; but if one says to you that your friend became wealthy, do not believe it until it has been proven.