Rashi on Numbers 20:18/רש"י על במדבר כ׳:י״ח

1פן בחרב אצא לקראתך LEST I COME OUT AGAINST THEE WITH THE SWORD — You pride yourselves on the “voice” which your father bequeathed you as a blessing, saying, “And we cried unto the Lord and He heard our voice” (cf. Rashi on v. 16); I, therefore, will come out against you with that which my father bequeathed me when he said, (Genesis 27:40) “And by thy sword shalt thou live” (Midrash Tanchuma, Beshalach 9 on בשלח)