C. F. Keil and Franz Delitzsch on Nehemiah 13:1-2

Neh 13:1-2 Public reading of the law, and separation from strangers. - Neh 13:1. At a public reading of the law, it was found written therein, that no Ammonite or Moabite should come into the congregation of God, because they met not the children of Israel with bread and with water, but hired Balaam to curse them, though God turned the curse into a blessing. This command, found in Deu 23:4-6, is given in full as to matter, though slightly abbreviated as to form. The sing. ישׂכּר relates to Balak king of Moab, Num 22:2., and the suffix of עליו to Israel as a nation; see the explanation of Deu 23:4.