Reference for Yoma 45:1
שאינו נוקם ונוטר כנחש אינו תלמיד חכם והכתיב (ויקרא יט, יח) לא תקום ולא תטור ההוא בממון הוא דכתיב דתניא איזו היא נקימה ואיזו היא נטירה נקימה אמר לו השאילני מגלך אמר לו לאו למחר אמר לו הוא השאילני קרדומך אמר לו איני משאילך כדרך שלא השאלתני זו היא נקימה
who does not avenge himself and retain anger like a serpent, is no [real] scholar.<span class="x" onmousemove="('comment',' Maharsha interprets this statement by reference to Gen. III, 15: And I will put enmity between thee and the woman, and between thy seed and her seed; they shall bruise thy head and thou shalt bruise their heel. The man will endeavour to crush the serpent so as to deprive it of its life: whereas the serpent retaliates by bruising only the heel, a non-vital part of the human body. Thus, 'serpent-like' the scholar should retaliate most moderately even when great wrong was done to him. - This proverb may also be a reaction to too humble a scholar, who by reason of his extreme forbearance seemingly encourages impudent and cruel people in their nefarious conduct. - Another suggested interpretation: just as great serpents swallowing their prey, moisten it with so much saliva as to be deprived of a sense of what, subjectively, they are eating, knowing only, objectively. that they are eating something, so should the scholar, against whom a wrong was committed, not endeavour to avenge himself subjectively, but to avenge objectively the wrong that was perpetrated. [Bacher (ZDMG, 1874, p. 6) relates this dictum to the one preceding: Any scholar who does not avenge himself like Nahash (which is the Hebrew for serpent) is no scholar. The reference is to a tradition preserved in a fragment of the Jerusalem Targum on Isa. XI, 2 that the condition made by Nahash for the offered covenant was that the Gileadites remove the injunction from the Torah barring the Ammonites from the congregation of Israel - an injunction which he considered an affront.]');"><sup>1</sup></span> But is it not written: Thou shalt not take vengeance nor bear any grudge?<span class="x" onmousemove="('comment',' Lev. XIX, 18.');"><sup>2</sup></span> - That refers to monetary affairs, for it has been taught: What is revenge and what is bearing a grudge?