2 Samuel 3:28-30
28 Afterwards, when David heard of it, he said, “I and my kingdom are forever innocent of the death of Avner the son of Ner. 29 Let it fall on the head of Yo’av and all his father’s family. May Yo’av’s family always have someone with a hemorrhage or tzara‘at, or who has to walk with a cane, or who dies by the sword or who lacks food.” 30 Thus Yo’av and Avishai his brother killed Avner, because he had killed their brother ‘Asah’el during the battle in Giv‘on.
Vengence outside the will of God has a devastating price, eventually costing Yo’av his life. We as believers should never try to do what is reserved for God.