Pirkei Avot 1:3 United Orthodox Synagogues

Tosafot:

Doesn't it say in Avot (1:3) "Do not be as servants who are serving the master in order to receive a reward? This is referring to a situation when if the good that one hopes for does not come, one regrets the charity that was given. However, one who does not regret, such a person is completely righteous. This is also alluded to in tractate Rosh Hashana (4a) and the first chapter of Bava Batra (10b).

Tosafot Yom Tov

BE NOT LIKE SERVANTS SERVING THE MASTER FOR PAY. Rav: rather, out of love alone. In other words, the mishna enjoins that the service be out of love alone, for this is the truest kind of service. It does not mean to say, however, that that service for pay is forbidden, as in either case he is serving G-d; for this reason our perfect Torah did not see unfit to mention rewards and punishments. One who serves in the hopes of earning reward or avoiding pain is simply not on the level of the one who serves out of love alone, whose service has no secondary intention whatsoever.
And the tanna wished to enjoin us to be among those who serve out of love alone, but not to exclude one who serves in the hopes of earning reward from the category of those who serve! This is not the case, as the Sages say in Bava Batra 10b: One who says, “I give this sela to charity that my son should live!” or “...that I should have a share in the world to come!” is perfectly righteous. Furthermore, if one takes the opposite position, one cuts the very legs out from under the nation of Israel!⁸ For “where is the weigher, where is the counter” (Isaiah 33:18) who shall say that so-and-so is one who truly serves out of love alone? And can it be good in G-d’s eyes that anyone who serves Him with the intent that the rewards promised by the Torah itself be fulfilled—that same Torah which has been communicated to us from His mouth—that such a one not receive his good lot on account of this? It pleases not their Master that people should say thus!
Rabbi Yehudah HaNassi says as much in Avot 2:1: Consider the loss incurred in doing a mitzvah against the reward for doing it, per my explanation there. Similarly, in 2:16: And you have a faithful taskmaster, who shall pay your wages. Cf. what I’ve written there on And you should know what reward awaits the righteous in the future. And we further see that there can be nothing wrong with this from the story of Azariah the brother of Simon, related in the mishna in Zevachim 1:2.
As mentioned above, the tanna of our mishna does not prohibit this, and I say that his own words prove it, which he chose with care in order that we shouldn’t misunderstand them. For why would he say “be not like servants serving the master for pay” when he could simply have said “do not serve for pay,” which would have gotten the point across to his students more succinctly? By saying “be not like servants who serve the master for pay” he taught that even those who serve for pay are servants at any rate, just that one should not be like them but greater than they, and should serve out of love alone.

Harav Gershon Shaul Yom-Tov Lipmann ben Nathan ha-Levi Heller (c. 1579 in Wallerstein, Bavaria – 19 August 1654 in Kraków), was a Bohemian rabbi and Talmudist, best known for writing a commentary on the Mishnah called the Tosefet Yom-Tov.