"Because of the cruelty and treachery of the Ammonites and Moabites toward Israel, God had declared through Moses that they should be forever shut out from the congregation of His people. See Deuteronomy 23:3-6 . In defiance of this word, the high priest had cast out the offerings stored in the chamber of God's house, to make a place for this representative of a proscribed race. Greater contempt for God could not have been shown than to confer such a favor on this enemy of God and His truth. PK 669.2"
"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: Because they met you not with bread and with water in the way, when ye came forth out of Egypt; and because they hired against thee Balaam the son of Beor of Pethor of Mesopotamia, to curse thee. Nevertheless the Lord thy God would not hearken unto Balaam; but the Lord thy God turned the curse into a blessing unto thee, because the Lord thy God loved thee. Thou shalt not seek their peace nor their prosperity all thy days for ever."
Ellen White directly references Deuteronomy 23:3-6 in this passage.
"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:"
The EGW passage explicitly references Deuteronomy 23:3-6 regarding the exclusion of Ammonites and Moabites from the congregation of Israel. It then describes how this commandment was violated, demonstrating a clear and direct connection.