Midrash su Salmi 106:28

Rabbi Yitzḥak interpreted the verse regarding the war with Midyan.²⁰⁶This war was conducted to avenge the fact that twenty-four thousand Israelites died in a plague as a result of idolatry they committed after being seduced by Moavite and Midyanite women. See Numbers chapter 25. You find that when Israel went out to the war with Midyan, they would enter in pairs to a woman, and one would blacken her face and one would remove her jewelry. She would say to them: ‘Are we not creations of the Holy One blessed be He, that you are doing this to us?’ The Israelites would say to them: ‘It it not enough for you that we received our punishment because of you?’ That is what is written: “The Lord said to Moses: Take all the leaders of the people, and hang them for the Lord opposite the sun, [and the enflamed wrath of the Lord will be withdrawn from Israel]” (Numbers 25:4). Rabbi Aivu said: What was the sin? “They cleaved to Baal Peor” (Psalms 106:28).
Rabbi Yitzḥak said: There was an incident involving a certain provincial woman, who had a Kushite maidservant who descended to draw water from the spring, she and her friend. She said to her friend: ‘My friend, tomorrow my master is going to divorce his wife and take me as a wife.’ [The friend] said to her: ‘Why?’ [The maidservant answered:] ‘Because he saw her hands blackened with coal.’ [The friend] said to her: ‘What a world-class fool, let your ears here what your mouth is saying. If his wife, who is exceedingly beloved to him, you say that he wishes to divorce her because he saw her hands blackened with coal, you who are completely black from your mother’s womb [and will be black] all your life, all the more so.’ So too, because the nations of the world taunt Israel and say: ‘This nation has exchanged their Glory,’ as it is stated: “They exchanged their glory [for the cast image of a grass-eating bull]” (Psalms 106:20), Israel says to them: ‘If we, who did so for a single moment, are liable in this manner, you, all the more so.’
Moreover, Israel says to the nations of the world: ‘We will tell you to what we are comparable; to the son of kings who went out to the wilderness outside the city and the sun beat down on his head and his face darkened. He entered the city, and with a little water and a little bathing from the bathhouse, his body whitened and he regained his previous beauty. So it is with us; [even] if the sun of idol worship has darkened us, you are darkened from your mother’s womb, for even when you were in your mother’s womb you worshipped idols. How so? When a pregnant woman enters her house of idol worship, she bows and prostrates herself to the idol, she and her son.’