If someone decided to help a poor family out by giving them a substantial amount of money (years worth) and then subsequently the poor gets yerusha or wins the lottery, according to the halacha does he need to return the money?
It would seem obvious from a derech eretz ,and hakaras hatov standpoint that he should give it back,but my question is can the donor bring him to bais din and have a claim?
Mishna Pea 8.8
היו לו מאתים חסר דינר, אפילו אלף נותנין לו כאחת, הרי זה יטול. היו ממושכנין לבעל חובו או לכתובת אשתו, הרי זה יטול.
Sota 21b:
What is the cunning rogue like? ... R`Abbahu says: He who gives a poor man a denar to bring his possessions to the total of two hundred zuz; for we have learnt (Mishna Pea 8.8); He who possesses two hundred zuz may not take gleanings, forgotten sheaves, the produce of the corner of the field, or the poor tithe; but should he lack one denar of the two hundred [zuz], even if a thousand persons give him [the gleanings, etc.] simultaneously, he may accept.
So, Halachically spoken he doesn't need to give it back. There is a discussion in Melechet Shelomo if the case is that 1000 persons give him simultaneously as the English translation shows or someone gives him 1000 dinar. The Tur and SA interpret the Mishna as the last case, but the Melechet Shlomo says that the first case is closest to the pshat of the Mishna. Following this Halacha, Kal vachomer if someone gives him a time before he becomes rich.
In Halacha Tur YD 253
יש לו מאתים זוז חסר דינר, אפילו נותנין לו אלף זוז בבת אחת, הרי זה יטול.
SA YD 253.1
ואם יש לו ר' זוז חסר דינר ואינו נושא ונותן בהם אפי' נותנים לו אלף זוז בבת אחת הרי זה יטול:
The only way of asking it back is to prove that it was given on a condition. You basically ask whether the giving was conditioned or not.
I assume that the Chazakah (the normal state of affairs) is that people give Tzedakah unconditionally, and we do follow the principle of "the burden of proof is on the plaintiff", so one who wants his money back needs to prove that he explicitly set a special condition (either in written or before witnesses).
For example that only the part of the charity that's used as long as they are below the poverty line is considered a Matana (free gift) but the part that is left when they cross the line will be considered debt.
The second part of your question is about Lifnei Shuras Hadin (whether the poor guy must be conscientious enough to return the money) the answer is that one can't claim Lifnei Mishuras Hadin in court unless it is a Paskened Halachah (as in a couple of cases with lost and found).
