The Gibeonites met the children of Israel, and although other nations were slaughtered, they were kept for hewers of wood and drawers of water. And of such value were they in God’s eyes that the family of Saul was destroyed for the wrong done to them. Where would you put them? Among the goats? But they were not slain, and they were avenged by the determination of God. Among the sheep? But holy Scripture says they were not of the same merit as the Israelites. You see then that they do indeed stand on the right hand but are of a far inferior grade.
Source: Against Jovinianus 2.33