צדקה

(1) These are the things that have no definite quantity: The corners [of the field]. First-fruits; [The offerings brought] on appearing [at the Temple on the three pilgrimage festivals]. The performance of righteous deeds; And the study of the torah. The following are the things for which a man enjoys the fruits in this world while the principal remains for him in the world to come: Honoring one’s father and mother; The performance of righteous deeds; And the making of peace between a person and his friend; And the study of the torah is equal to them all.

(6) This measure (the maaser ani or poor tithe) was stated for the priest, Levite and Israelite alike. If he was saving some [to give to his poor relatives], he can retain half and give the other half away. If he has only a small amount, then he must place it before them and they then divide it among themselves.

(7) They may not give a poor person wandering from place to place less than a loaf worth a pundion at a time when four seahs [of wheat cost] one sela. If he spends the night [at a place], they must give him the cost of what he needs for the night. If he stays over Shabbat they must give him enough food for three meals. He who has the money for two meals, he may not take anything from the charity dish. And if he has enough money for fourteen meals, he may not take any support from the communal fund. The communal fund is collected by two and distributed by three people.

(8) One who possesses two hundred zuz, may not take gleanings” the forgotten sheaf, peah or the poor man’s tithe. If he possesses two hundred minus one denar, then even if a thousand [men] each give him at the same time, he may accept. If he had [two hundred zuz] mortgaged to a creditor or to his wife’s ketubah, he may take. They do not force him to sell his house or his tools.

(3) We are commanded to give a poor person according to what he lacks. If he lacks clothes, we should clothe him. If he lacks household utensils, we should purchase them for him. If he is unmarried, we should help him marry. And for an unmarried woman, we should find a husband for her.
Even if the personal habit of this poor person was to ride on a horse and to have a servant run before him to announce his coming. and then he became impoverished and lost his wealth, we should buy a horse for him to ride and a servant to run before him. Ketubot 67b relates that a person from a dignified family became impoverished and the great Sage Hillel would hire a servant to run before him and announce his coming. Once Hillel could not find such a servant and performed this service himself. [This is implied by Deuteronomy 15:8 which] speaks [of providing him with] "enough to [fill the] lack that he feels." Because of his previous lifestyle, this person feels a severe lack if he does not have these conveniences. You are commanded to fill his lack, but you are not obligated to enrich him. Thus there are times when providing a certain person with what he feels are his needs will require a greater expense than providing another with what he views as luxuries.

(5) When a poor person comes and asks for his needs to be met and the giver does not have the financial capacity, he should give him according to his financial capacity.
How much? The most desirable way of performing the mitzvah is to give one fifth of one's financial resources.This also reflects an upper limit. As Ketubot 50a states: "Even a person who distributes money to charity with largess should not distribute more than a fifth." This concept is derived from Jacob's vow to tithe (Genesis 28:22 . There the verb which conveys the promise to tithe is repeated, allowing for the concept of giving two tithes. See also Hilchot Arachin 8:13 which cites Leviticus 27:28 which speaks of a person designating a dedication offering "from all that is his." The Rambam continues:
[Implied is that he should not give] "all that is his," as our Sages explained. This is not piety, but foolishness, for he will lose all his money and become dependent on others. We should not show mercy to such a person. In a similar vein, our Sages said: "A man of foolish piety is among those who destroy the world." Instead, a person who distributes his money for mitzvot should not distribute more than a fifth, and he should conduct himself as our Prophets advised [cf. Psalms 112:5]: "He arranges his affairs with judgment," both with regard to matters involving Torah and worldly concerns.
Yayin Malchut notes that in his Commentary to the Mishnah (Pe'ah 1:1), the Rambam writes that as an act of piety, a person may give more than a fifth. Nevertheless, there is not necessarily a contradiction between the two. In his Commentary to the Mishnah, the Rambam is speaking about giving to a needy person who asks for alms. In response to that acute need, one may give more that a fifth. Here the Rambam is speaking about giving to charity when there is no acute need. Hence a limit can be established. See also Ketubot 67b which states that these restrictions apply during a person's lifetime. He may leave a greater percentage of his resources to charity in his will.
In Iggeret HaTeshuvah, Rav Shneur Zalman of Liadi states that one may give more than a fifth of his resources to charity to atone for his sins, for just as one is not concerned with the amount one gives when it comes to healing a physical wound or blemish, so too, one should not be worried about cost when healing a spiritual blemish.

Giving one tenth is an ordinary measure.13The Sifri derives this from the fact that Deuteronomy 14:22, the verse that conveys the Biblical command to tithe repeats the verb, implying an obligation to tithe - not only one's produce - but all income. Giving less [than that] reflects parsimony. A person should never refrain from giving less than a third of a shekel a year. This is slightly less than seven grams of silver. A person who gives less than this has not fulfilled the mitzvah. Even a poor person who derives his livelihood from charity is obligated to give charity to another person.

(1) In every city where Jews live, they are obligated to appoint faithful,1See Chapter 10, the conclusion of Halachah 8. men of renown as trustees of a charitable fund. They should circulate among the people from Friday to Friday and take from each person what is appropriate for him to give and the assessment made upon him. They then allocate the money from Friday to Friday, giving each poor person sufficient food for seven days. This is called the kupah.2The term literally means "container" and refers to the charity box in which donations were placed and by extension, to the fund financed by those collections.

(2) Similarly, we appoint trustees who take bread, different types of food, fruit, or money from every courtyard from those who make a spontaneous donation and divide what was collected among the poor in the evening, giving each poor person sustenance for that day. This is called the tamchui.3In his Commentary to the Mishnah (Keilim 13:3), the Rambam defines this term as a pot with compartments.

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(3) We have never seen nor heard of a Jewish community that does not have a kupah for charity. A tamchui, by contrast, exists in some communities, but not in others. The common practice at present is that the trustees of the kupah circulate [among the community and collect] every day and divide [the proceeds] every Friday.4So that the poor will have their Sabbath needs provided for.