Numbers 20:18

פן 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)

וַיֹּ֤אמֶר אֵלָיו֙ אֱד֔וֹם לֹ֥א תַעֲבֹ֖ר בִּ֑י פֶּן־בַּחֶ֖רֶב אֵצֵ֥א לִקְרָאתֶֽךָ׃

And Edom said to him, Thou shalt not pass by me, lest I come out against thee with the sword.