Ecclesiastes Rabbah 6:1

¹“There is an evil that I have seen under the sun, and it is prevalent among men” (Ecclesiastes 6:1). “There is an evil that I have seen under the sun.” Rabbi Shmuel bar Ami said: This is the thought of swindlers, like one who mixes water into wine, poppy oil into [olive] oil, spring water into honey, donkey milk into balsam oil, sap into myrrh, grape leaves into valuable pollen, water dyed red into fish brine, vetch into pepper, [or one who uses] a scale beam that is long on one side and short on the other side. Regarding all these, Rabbi Yoḥanan ben Zakkai said: Woe is me if I say it, and woe is me if I do not say it. If I say it, perhaps the swindlers will learn [new techniques for swindling]. If I do not say it, the swindlers will say: The Torah scholars are not conversant in our handiwork. Ultimately, he said it, “for the ways of the Lord are straight, the righteous walk in them [and the transgressors stumble in them]” (Hosea 14:10).