הלכה על יבמות 152:2

From the laws of the commandment is that which they, may their memory be blessed, said (Yevamot 76b) that specifically the males of the Children of Ammon and Moav - them and their sons forever - are the ones forbidden to come into the congregation, but the females are permitted immediately when they convert. And they said in explanation of this that it is since it is the way of the man to greet, but not the females; which is to say that their hand was not in this villainy when [the men] did not greet Israel with bread and water - since it is not the way of a woman to go out. And God would not twist justice to punish the woman for the villainy of the man - God forbid, that God would [allow such] evil. And the rest of its details are elucidated in the eighth chapter of Yevamot and at the end of Kiddushin (see Tur, Even HaEzer 4).