Deuteronomy 23:3-4

3Ammonite and Moabite people also cannot join with the Lord's people when they come together to worship him. Even the tenth generation of their descendants can never do this.

4The people of those nations refused to help you when you were leaving Egypt. They did not give you food or water. Also, they paid Beor's son Balaam to curse you. He came from Pethor in Mesopotamia.