An Ammonite or Moabite shall not enter. According to Rashi, “shall not marry an Israelitish woman.” It must be remembered that the children, according to Jewish law, follow the father, not the mother. The case of Ruth would not, therefore, be touched by this precept.
Related Commentaries of Deuteronomy 23:3
Deuteronomy 23:3
3 An Ammonite or Moabite shall not enter into the congregation of the LORD; even to their tenth generation shall they not enter into the congregation of the LORD for ever: