Deuteronomy 2:9
And the LORD said unto me, Distress not the Moabites, neither contend with them in battle: for I will not give thee of their land for a possession; because I have given Ar unto the children of Lot for a possession. And the LORD said unto me, Distress not the Moabites, neither contend with them in battle: for I will not give thee of their land for a possession; because I have given Ar unto the children of Lot for a possession.
God directed Israel not to distress, harass or molest the Moabites and not to contend with them in battle or fight against them. Moab was shielded from attack because the Moabites were descended from Lot. God had given Ar to the children and descendants of Lot as their allotted possession, and for that reason he would give Israel none of Moab's land for a possession. Israel therefore journeyed on to the east of Moab instead of taking its territory.