Numbers 32:1-6, 16-27
Now the sons of Reuben and the sons of Gad had a very great multitude of cattle; and they saw the land of Jazer and the land of Gilead, and behold, the place was a place for cattle. So the sons of Gad and the sons of Reuben came and said to Moses and to Elea'zar the priest and to the leaders of the congregation, "At'aroth, Dibon, Jazer, Nimrah, Heshbon, Elea'leh, Sebam, Nebo, and Be'on, the land which the LORD smote before the congregation of Israel, is a land for cattle; and your servants have cattle."
And they said, "If we have found favor in your sight, let this land be given to your servants for a possession; do not take us across the Jordan." But Moses said to the sons of Gad and to the sons of Reuben, "Shall your brethren go to the war while you sit here?
Then they came near to him, and said, "We will build sheepfolds here for our flocks, and cities for our little ones, but we will take up arms, ready to go before the people of Israel, until we have brought them to their place; and our little ones shall live in the fortified cities because of the inhabitants of the land. We will not return to our homes until the people of Israel have inherited each his inheritance. For we will not inherit with them on the other side of the Jordan and beyond; because our inheritance has come to us on this side of the Jordan to the east."
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. But if you will not do so, behold, you have sinned against the LORD; and be sure your sin will find you out. Build cities for your little ones, and folds for your sheep; and do what you have promised."
And the sons of Gad and the sons of Reuben said to Moses, "Your servants will do as my lord commands. Our little ones, our wives, our flocks, and all our cattle, shall remain there in the cities of Gilead; but your servants will pass over, every man who is armed for war, before the LORD to battle, as my lord orders."