Numbers 32:20-22

So Moses said to them, “If you will do this, if you will take up arms to go before the LORD for the war, and every armed man of you will pass over the Jordan before the LORD, until he has driven out his enemies from before him and the land is subdued before the LORD; then after that you shall return and be free of obligation to the LORD and to Israel, and this land shall be your possession before the LORD.