Where is an allusion in the Torah to this “curse”?
Why did the Torah need to write "Hin Tzedek" (Vayikra 19,36)? (Hin and Eifah are measures of volume. One's measures must be accurate, lest he use them to swindle when buying or selling.) It already says "Eifah Tzedek"!
Rabbi Yosi answers that this teaches that your 'Hen' and 'Lav' (when you say yes or no) must be just and fulfill your words.