Rashi on Isaiah
and anyone who takes refuge with the people of the city to be included with them in the siege, shall fall by the sword when the city capitulates. נִסְפֶּה is an expression similar to (Deut. 29:18): “To add the unintentional sins to the lustful ones (סְפוֹת)”; (infra 29:1) “Add year upon year (סְפוּ)”; (Jer. 7:21) “Add (סְפוּ) to your sacrifices.” [akojjlir in O.F.], to join.