Bava Kama 38b
א"ר חייא בר אבא א"ר יוחנן
אין הקב"ה מקפח שכר כל בריה
Lot's first born daughter named her child מואב thus recalling
she bore him from her father.
Lot's second daughter named her child בן עמי which does not explicitly recall the child was from her father.
For being more discreet than her older sister, she was rewarded.
In the Hakdama to the Igros Moshe (O.Ch.5) there is a very interesting story told by Reb Moshe zt"l.
Reb Moshe went to be Mevaker Choleh in Luban a sick person whose tongue had swelled up.
He told Reb Moshe the reason why he contacted this disease.
He said he had a Kushya.
"How is it, that the Mashiach will be an offspring of these two women who weren't even ashamed to name their children and publicize having relations with their own father ?"
One day he had a dream, two elderly women came to him and claimed to be the daughters of Lot. They told him they heard his complaint and want to respond.
They said they could have easily claimed that the children were born by an immaculate conception.
They intentionally named them עמון ומואב (embarrassing themselves) to publicize there is no such thing as an
They were therefore rewarded that the True Mashiach will come from them.
They also told him that he was being punished for speaking badly about them.
After he finished telling the story to Reb Moshe he turned to the other side and died.