מדרש על עובדיה 1:10

Weapons of violence. He said to them: The weapons in your possession are weapons of violence stolen from Esau, of whom it is said: By the sword shalt thou live (ibid. 27:40). These are weapons of violence, and violence is associated with Esau, as it is said: For the violence done to thy brother Jacob, shame shall cover thee, and thou shalt be cut off forever (Obad. 10).