מדרש אויף דברי הימים ב 21:13

[2] Another interpretation: "and Abimelech acted justly." As it says, 'He who digs a pit will fall into it, and whoever rolls a stone, it will come back on him.' (Proverbs 26:27) Anyone who kills his brother with a staff, Jehoram stood up and killed the sons of his father's belly, as it says, 'Moreover, you have killed your brothers, your father's household, who were better than you.' (2 Chronicles 21:13) And because he killed the sons of his father's belly, therefore his bowels came out with his sickness, as it says, 'And they went on for days, and at the end of two years, his bowels came out because of his sickness.' (2 Chronicles 21:19) Why does it say, 'He who digs a pit will fall into it, and whoever rolls a stone, it will come back on him'? Cain killed his brother with a stone, as it says, 'And Cain rose up against Abel his brother and killed him.' (Genesis 4:8) And how did he kill him? He took a stone and struck him on all his organs with blows until he died. How do we know this? Because Lamech said to his wives, 'I have killed a man for wounding me.' (Genesis 4:23) And even Cain was killed with a stone, as it says, 'And Cain went out.' (Genesis 4:16) A stone fell on him and killed him. Why does it say, 'And whoever rolls a stone, it will come back on him'? Abimelech also killed his brothers with a stone, as it says, 'And he killed them on one stone.' (Judges 9:5) And he was also killed with a stone, as it says, 'And a certain woman threw an upper millstone upon Abimelech's head, and crushed his skull.' (Judges 9:53) Woe to him who rolls a stone, for it will come back on him."