Numbers 32:16-20

And they came near unto him, and said, We will build sheepfolds here for our cattle, and cities for our little ones:

But we ourselves will go ready armed before the children of Israel, until we have brought them unto their place: and our little ones shall dwell in the fenced cities because of the inhabitants of the land.

We will not return unto our houses, until the children of Israel have inherited every man his inheritance.

For we will not inherit with them on yonder side Jordan, or forward; because our inheritance is fallen to us on this side Jordan eastward.

And Moses said unto them, If ye will do this thing, if ye will go armed before the LORD to war,