Reference for Bava Kamma 178:7

כגון דלא נפישא כתובתה מכתובה דאורייתא דהוי חבליה ארבעה זוזי דמשום ארבעה זוזי לא מפסיד עשרים וחמשה

and she should assign the difference to the husband as compensation for the injury? [This could not be done where,] e.g. the amount of her <i>kethubah</i> did not exceed that of the ordinary <i>kethubah</i> fixed by the Law and the compensation for the injury was assessed to be four <i>zuz</i>, as it is pretty certain that for four <i>zuz</i> he will not risk losing twenty-five [<i>sela'</i>].<span class="x" onmousemove="('comment',' = 100 zuz, which is the minimum amount of a kethubah even in the case of a non-virgin; v. Keth. I, 2. ');">⁷</span>

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