How Much to Spend on a Mitzvah and the Limit of One Fifth

There we learned: These are the things that have no fixed measure: deeds of loving-kindness, and so on. This that was stated [that they have no measure] refers to service with one's body; but with one's money there is a measure. And this accords with what Reish Lakish said: They voted in Usha that a person should set aside a fifth of his property for a commandment. Up to where? Rabbi Gamliel bar Inyana and Rabbi Abba bar Kahana: one said, up to the amount of terumah and the tithe of the tithe; and one said, [as in] "Honor the LORD with your wealth and with the first of all your produce" (Proverbs 3:9), like the first of all your produce. Rabbi Gamliel bar Inyana inquired before Rabbi Mana: If it is a fifth every year, then over five years he loses all of it. He said to him: At the outset it is from the principal; from there onward it is from the profit. Rav Huna said: For commandments, just as for all commandments it is up to one-third; they thought to say, for all commandments up to one-third. Rabbi Avin said: even for a single commandment. Rabbi Chanina in the name of the Rabbis there: a third of the price. How so? A person buys one commandment-object and then sees another, finer one; up to how much do they impose upon him? Up to a third. Rabbi Ishmael taught: "This is my God, and I will glorify Him": beautify yourself before Him with the commandments, and so on.