Nombres 12:1

[Miriam] spoke. דִּבּוּר always connotes harshness, as it says, “The man who rules the land spoke harshly with us.” But אֲמִירָה always connotes pleading, as it says, “He said, please, my brothers, do not be wicked,” “He said, please hear my words.” נָא always connotes a request.

Miriam and Aharon spoke. She opened the discussion first, so Scripture gives her precedence. How did Miriam know that Moshe separated from his wife? R’ Noson says: Miriam was at Tziporah’s side when Moshe was told that Eldad and Meidad were prophesying in the camp. When Tziporah heard, she said, ‘Woe to their wives if they become attached to prophecy, because they will separate from their wives the way my husband separated from me.’ Miriam knew from there, and she told Aharon. Now if Miriam, who did not intend to slander him, was punished this way, certainly someone who relates slander about his fellow.

The Cushite woman. This teaches that everyone agreed to her beauty, just as everyone agrees to the blackness of the Cushite.

Cushite. [כּוּשִׁית is] numerically equivalent to יְפַת מַרְאֶה, (“beautiful in appearance.”)

Concerning the woman. Concerning her divorce.

For, he married a Cushite woman. What does the Torah teach? You find a woman beautiful in appearance but not beautiful in deed; in deed, but not in appearance. But this one was beautiful in everything.

The Cushite woman. Because of her beauty, she was called “Cushite,” like a man who calls his attractive son “Cushite” to ward off the power of the evil eye over him.

For, he married a Cushite woman. And now divorced her.

And Miriam and Aharon spake against Mosheh words that were not becoming with respect to the Kushaitha whom the Kushaee had caused Mosheh to take when he had fled from Pharoh, but whom he had sent away because they had given him the queen of Kush, and he had sent her away.

Miriam and Aharon spoke. She spoke, and Aharon agreed with her or was silent, and therefore he was punished.

הכושית, from one of the tribes going back to Cham.

כי אשה כושית לקח, as reported in the biography of Moses (compare Yalkut Shimoni, edition by Heiman-Shiloni on Exodus page 34, glossary 18) According to that version, Moses ruled for 40 years as king over the land of Cush, took himself a woman as his queen but never slept with her, as reported there. Miriam and Aaron were never aware of the fact that Moses had not consummated that union. This is the plain meaning of our verse.
If, as some believe, Miriam and Aaron spoke about Moses and Tzipporah, what need was there for the Torah to describe Moses’ wife as אשה כושית when everyone is well aware that Moses married Tzipporah the daughter of Yitro who was a Midianite, not a Cushite. Tzipporah could not have been described as Cushite seeing that the Cushites are descended from Cham, and the Midianites are descendents of the sons of Keturah, Avraham’s concubine, who bore 6 sons for him one of them being Midian. [Rash’bam’s argument is tenuous, for if Keturah was the same person as Hagar, according to most commentators, seeing that Hagar was an Egyptian, a woman descended from her could be described as Cushite, seeing that Mitzrayim, Egypt, was a descendant of Cham, also. Ed.]

ותדבר מרים ואהרן במשה, “Miriam and Aaron spoke critically about Moses.” Seeing that it is a fact that women indulge more in loose talk, Miriam is mentioned here first, seeing that she was a woman.

כי אשה כושית לקח, “for he had married a woman from the land of Cush.” (Ethiopia) According to Moses’ biography, Moses had been king in that country and his wife had been a queen in her own right previously. Moses had ruled over that land for a period of forty years (before coming to Midian) This is why the Torah reported Miriam and Aaron as speaking critically only of Moses (“did G–d only speak with Moses?”) They thought that seeing that G–d had spoken with Moses, Moses had felt that no Jewish woman was good enough for him to marry, i.e. that he had given himself airs. They did not criticise Moses for having married Tzipporah, as he had done so in circumstances when he was a refugee from Egyptian justice at the time.