מדרש על שופטים 1:3

"And to his people shall You bring him": For he (Judah) had drawn him (Shimon) near to himself for inheritance (of the land), as it is written (Judges 1:3) "and Judah said to Shimon his brother: "Go up with me (in battle) for my portion." And sections fell (for inheritance) from the inheritance of the children of Judah to that of the children of Shimon (viz. Joshua 19:9).