Pirkei Avot §avot_01_03: Antigonus a man of Socho received [the oral tradition] from Shimon the Righte...

Antigonus a man of Socho received [the oral tradition] from Shimon the Righteous. He used to say: do not be like servants who serve the master in the expectation of receiving a reward, but be like servants who serve the master without the expectation of receiving a reward, and let the fear of Heaven be upon you.