מדרש אויף במדבר 24:9

The Holy One, blessed be He, said: You saved four lives from fire and death when you ignored the command: Bring her forth, and let her be burned (ibid. 38:24). Therefore, I will rescue four of your descendants, Daniel, Hananiah, Mishael, and Azariah form the furnace and the lion’s den. He called Judah by four different names: a lion, a whelp, and he lay down as a lion, and as a lioness (Num. 24:9).

“Peoples will serve you, and nations will prostrate themselves to you. Be a lord to your brethren, and your mother’s sons will prostrate themselves to you. Cursed be one who curses you, and blessed be one who blesses you” (Genesis 27:29).
“Peoples will serve you” – these are the seventy nations. “And nations will prostrate themselves to you” – these are the descendants of Ishmael and the sons of Ketura, in whose regard it is written: “Ashurim, Letushim, and Leumim” (Genesis 25:3). “Be a lord to your brethren” – this is Esau and his chieftains. “And your mother’s sons will prostrate themselves to you” – here it says: “And your mother’s sons will prostrate themselves to you,” but elsewhere it says: “And your father’s sons will prostrate themselves to you” (Genesis 49:8). It is that Jacob, because he took four wives, Leah, Rachel, Zilpa, and Bilha, he says: “Your father’s sons.” Isaac took Rebecca, he said: “Your mother’s sons.”
“Cursed be one who curses you…” – and elsewhere it says: “Those who bless you are blessed, and those who curse you are cursed” (Numbers 24:9). It is that Bilam, because he was a hater, began with a blessing and concluded with a curse. Yitzḥak, who was a lover, opened with a curse and concluded with a blessing.
Rabbi Yitzḥak bar Rabbi Ḥiyya said: The wicked, because their beginning is tranquility and their end is suffering, they begin with blessing and end with curse. The righteous, because their beginning is suffering and their end is tranquility, they begin with curse and end with blessing: “Cursed be one who curses you, and blessed be one who blesses you.”

Another matter, “blessed be one who blesses you” – it is taught: An idol worshiper who blesses the Name, one answers amen after him; with the Name, one does not answer amen after him.⁶If a gentile blesses God, one should answer ‘Amen.’ If he blesses a Jew using the name of God, one should not answer ‘Amen,’ to indicate that his blessing does not help (Etz Yosef). Rabbi Tanḥuma said: If one idolater blesses you, answer amen after him, as it is written: “You shall be blessed more than all the peoples [mikol haamim]” (Deuteronomy 7:14).⁷Literally – “from all the nations.” A certain idolater encountered Rabbi Yishmael and blessed him. He said to him: ‘The response is already stated.’ A certain idolater encountered Rabbi Yishmael and cursed him. He said to him: ‘The response is already stated.’ They said to him: ‘What you said to this one, you said to that one.’ He said to them: ‘So it is written: “Those who bless you are blessed, and those who curse you are cursed”’ (Numbers 24:9).