Midrash sur Les Nombres 24:22

Corresponding to the name of Ishmael's son Kedar, the sons of Kedar were so called, as it is said, "Of Kedar, and of the kingdoms of Hazor" (Jer. 49:28). Corresponding to the name of Ishmael's son "Kedemah" (Gen. 25:15), the "sons of Ḳedem" were so called. Because they dwelt in the territory belonging to Cain, his children were called "sons of Cain," as it is said, "Now Heber the Kenite had separated himself from Cain" (Judg. 4:11). Were not all the sons of Cain cut off by the waters of the Flood? But because they dwelt in the territory of the children of Cain, his children were called "sons of Cain," as it is said, "Nevertheless || Cain shall be wasted, as long as Asshur shall dwell in thy place" (Num. 24:22). "Nevertheless Cain shall be wasted away" by fire, through the seed of Ishmael, the latter shall cause the kingdom of Assyria to cease.