Numbers 32:20-22

Then Moses said to them, If you will do this, arming yourselves to go before the Lord to the war, Every armed man of you going across Jordan before the Lord till he has overcome and sent in flight all who are against him, And the land is under the rule of the Lord: then after that you may come back, having done no wrong to the Lord and to Israel; and this land will be yours for your heritage before the Lord.