Matthew Poole and continuators on 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 .

This may be understood either 1. Of the Males onely, or the children of such fathers, as Interpreters commonly take it. Or rather 2. Of Females also, or of all that were born either of such Fathers or Mothers, as may be gathered from Ezra. 10. and Nehem. 13. where the Children of strange Wives were separated from Israel no less than the Children of strange fathers. And it is an allowed maxime, that the birth follows the belly. And whereas the Children of Rahab and Ruth are produced to the contrary, it may be said as it was before, that these were extraordinary instances, and that God when he pleased might exempt any particular person of them from this curse, though the Israelites might not do so.

So it seems to note the Immutability and perpetuity of this Law, that it should be inviolably observed in all succeeding ages, and not dispensed with for any merit in the persons, or any pretence whatsoever. But why then should this clause be added onely here, seeing the foregoing laws are as inviolable as this? It seems therefore to extend the duration of this exclusion of them from the Congregation of the Lord beyond what was said at first, and to be added by way of aggravation, even to their tenth generation shall they not enter—yea, even for ever; i. e. they shall never enter, as it is expressed, without any mention of the tenth Generation, Neh. 13. 1. that they should not come into the Congregation of God for ever.

Marginal references: Neh. 13. 1.