Orchot Tzadikim, Sha'ar Hanedivut (The Gate of Generosity)

Our sages of blessed memory have stated further that the trait of generosity resides in habit, for one is not called generous until one becomes accustomed to giving, in every time and season, according to one's ability. For one who gives to a deserving person 1,000 gold pieces at once is not as generous as one who gives 1,000 gold pieces one by one, each gold piece to an appropriate recipient. For one who gives 1,000 gold pieces at once is seized with a fit of generosity that afterwards departs . . . About this, the sages said, "all is according to the abundance of deeds" (Mishnah Avot 3:15). They did not say "according to the greatness of deed." [translation by Rabbi Jill Jacobs]