תלמוד על אבות 2:7

There is a story of Hillel the Elder, that he was walking on the road, and he came upon people who were carrying wheat. He said to them: How much would a se’ah³A se’ah is a grain measure, roughly equivalent to 1.9 gallons. cost? They said to him: Two dinars. He came upon another group, and asked them: How much would a se’ah cost? They said to him: Three dinars. [He said: But the first group told me it was only two!] They said to him: You stupid Babylonian! Don’t you know that the reward is in proportion to the struggle? He said them: You fools! (And empty ones!) Because I constantly instruct you [that the reward is commensurate with the toil], you are replying so [i.e. in kind]? Thus Hillel the Elder did to them to bring them back to good behavior.
It was also he who saw a skull floating on the water and said to it: Since you drowned others, you were drowned. And those who drowned you will also be drowned.