Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[166] At this time it was that the two tribes of Gad and Reuben, and the half tribe of Manasseh, abounded in a multitude of cattle, as well as in all other kinds of prosperity; whence they had a meeting, and in a body came and besought Moses to give them, as their peculiar portion, that land of the Amorites which they had taken by right of war, because it was fruitful, and good for feeding of cattle; but Moses, supposing that they were afraid of fighting with the Canaanites, and invented this provision for their cattle as a handsome excuse for avoiding that war, he called them arrant cowards, and said they had only contrived a decent excuse for that cowardice; and that they had a mind to live in luxury and ease, while all the rest were laboring with great pains to obtain the land they were desirous to have; and that they were not willing to march along, and undergo the remaining hard service, whereby they were, under the Divine promise, to pass over Jordan, and overcome those our enemies which God had shown them, and so obtain their land. But these tribes, when they saw that Moses was angry with them, and when they could not deny but he had a just cause to be displeased at their petition, made an apology for themselves; and said, that it was not on account of their fear of dangers, nor on account of their laziness, that they made this request to him, but that they might leave the prey they had gotten in places of safety, and thereby might be more expedite, and ready to undergo difficulties, and to fight battles. They added this also, that when they had built cities, wherein they might preserve their children, and wives, and possessions, if he would bestow them upon them, they would go along with the rest of the army. Hereupon Moses was pleased with what they said; so he called for Eleazar the high priest, and Joshua, and the chief of the tribes, and permitted these tribes to possess the land of the Amorites; but upon this condition, that they should join with their kinsmen in the war until all things were settled. Upon which condition they took possession of the country, and built them strong cities, and put into them their children and their wives, and whatsoever else they had that might be an impediment to the labors of their future marches.