הלכה אויף דברים 23:4

Intercourse prohibitions according to the Torah for which there is no punishment of karet are called “negative prohibitions”. They are also called “holy prohibitions”. There are nine [such prohibitions] and they are: a widow to a high priest, a divorced woman or zona or ḥalala to a high priest or to an ordinary priest, a mamzeret to an Israelite man, an Israelite woman to a mamzer, an Israelite woman to an Ammonite or Moabite man, an Israelite woman to one with crushed [genitals], or severed [genitals], one’s ex-wife after she has remarried, one’s yevama who married a stranger while still under the yavam’s control. A ḥalutza is like a divorced woman and is forbidden to a priest according to Rabbinic law. The Gibeonites are like mamzerim, whether male or female, and they are prohibited according to Rabbinic law. The Gibeonites will be explained in the Laws of Forbidden Intercourse.

Not to intermarry with idolaters, as it is said, “Neither shalt thou make marriages with them” (Deut. 7:3).

That an Ammonite or Moabite shall never marry the daughter of an Israelite, as it is said, “An Ammonite or Moabite shall not enter (into the congregation of the Lord)” (Deut. 23:4).