Numbers 32:30

So concerning them Moses commanded Eleazar the priest, and Joshua the son of Nun, and the chief fathers of the tribes of the children of Israel:

And Moses said unto them, If the children of Gad and the children of Reuben will pass with you over Jordan, every man armed to battle, before the LORD, and the land shall be subdued before you; then ye shall give them the land of Gilead for a possession:

And the children of Gad and the children of Reuben answered, saying, As the LORD hath said unto thy servants, so will we do.

We will pass over armed before the LORD into the land of Canaan, that the possession of our inheritance on this side Jordan may be ours.