Musar for Shevuot 71:2
אמר רבי אבהו מנין לאלה שהיא שבועה שנאמר (יחזקאל יז, יג) ויבא אתו באלה וגו' וכתיב (דברי הימים ב לו, יג) וגם במלך נבוכדנצר מרד אשר השביעו באלהים
and heareth the cursing; and heareth the voice.<span class="x" onmousemove="('comment',' The verse could have said: and heareth the alah (cursing) i.e., oath accompanied by a curse; the word voice is superfluous, so we deduce that it implies even a voice (i.e., oath) unaccompanied by a curse. [The interpretation adopted here follows Rashi who, apart from the reading of MS.M. referred to in n. 5, which he seemed to have had, deletes the words: 'an alah unaccompanied by an oath like an alah with an oath,' which are placed in cur. edd. in brackets. These words are, however, retained by Nahmanides in his novellae on Shebu'oth, and other texts. Adopting this reading, preference is to be given to the reading 'with an oath' of cur. edd. (v. n. 5) and the whole passage must be taken as a continuation of the discussion relating to the source whence the Rabbis derive that 'alah' implies an oath, and is to be interpreted thus: 'But there it is written the oath of alah (how then can there be derived from that verse that alah by itself denotes an oath) ? - Thus he (the Tanna of the Baraitha) means: 'alah'; alah can only be with an oath, and thus it says: 'and the priest . . of alah.' And whence do we know to make an alah unaccompanied by an oath like an alah with an oath, and an oath unaccompanied by an alah like an oath accompanied etc. - Thus is afforded the source whence the Rabbis deduce that alah implies an oath.]');"><sup>2</sup></span> R'Abbahu said: Whence do we know that alah implies an oath?