As discussed above, it is proper for every person to regularly set aside a certain sum of money in a fund so that it will be available for the mitzvah of giving loans. And so that it will not be difficult to have these sums, it is proper that the person accustom himself to separating a tenth of any profit that the Holy One bestows him. From that, he should give two-thirds as actual tzedakah to the poor — for this is something that is commonly needed — and he should keep one third for fulfilling the mitzvah of bestowing-kindness by extending loans to those who need it.
The idea of separating a tenth of one’s money (ma’aser kesafim) is a very great deed. We see this in the lesson taught by the Sages on the words, You shall tithe [“Aser t’aser”] (Devarim 14:22) — “Separate a tenth [aser] so that you will become wealthy [tis’asher].” We are not allowed to test Hashem in any matter except for this matter of giving a tenth, as it is written in the words of the prophet: Bring all the tithes into the storage house, and let it be sustenance in My Temple. Test Me, if you will, with this, says Hashem, Master of Legions, [see] if I do not open up for you the windows of the heavens and pour out upon you blessing without end (Malachi 3:10).