Pras vs. Sachar — Eruvin 72b
תלמוד בבלי מסכת עירובין דף עב/ב
רב יהודה אמר רב במקבלי פרס שנו
In Pirkei Avos (1:3), Antigonus of Socho tells us that we should not serve Hashem as slaves who toil in order to receive a פרס, but like slaves who serve Hashem with no ulterior motivation.
From this passage in our Gemara and subsequently 73a it seems that pras connotes sustenance in this world. Indeed, Rashi to Avos (loc. cit.) explains that the reason one should not serve Hashem in order to receive a pras is because there is no reward in this world for mitzvos (דשכר מצוה בהאי עלמא ליכא).
Thus, writes R' Tzadok HaKohen of (Divrei Sofrim §4), Antigonus actually meant to
admonish his students not to seek reward for their mitzvos in this world.
Moreover, states Reb Tzadok, even when a person's intent is to seek reward in the World to Come, if his intent is only to attain a "spot" in, and the "benefits" of the World to Come, then that too falls into the category of seeking to receive a pras. Rather, one's intent should be to merit enjoying the radiance of the Shechinah — which is the true sachar of the World to Come. When that is the intent of one's performance of a mitzvah, the mitzvah brings one to Teshuvah, to Ahavas Hashem and to Dveykus.
Based on this dichotomy between pras and sachar, Reb Tzadok explains several difficult Ma'amarei Chazal — some that indicate that Gedolei HaDoros would serve Hashem with the intent to receive sachar, and some that encourage Avodas Hashem with the intent to receive sachar. For example, earlier in the mesechta (28b) we saw that when he was feeling weak, R' Zeira would sit outside the Beis Medrash to rise before the rabbis entering and exiting in order "to receive a reward [sachar]." It is only the quest of pras that is not proper. The quest for sachar — for Dveykus — is, in fact, the primary purpose of mitzvos, and to seek that sachar is to do a mitzvah lishmah.