Miriam and Aaron criticized Moses because of the Cushite woman he married (for he had married a Cushite woman).
References for Numbers 12:1
They said, "Does the Lord speak only through Moses? Does He not also speak through us?" And the Lord heard [it].
Moses was a very humble man, more so than any man on the face of the earth.
Suddenly the Lord said to Moses, Aaron, and Miriam, "You three come out to the tent of meeting." So the three of them went out.
Then the Lord descended in a pillar of cloud, stood at the entrance to the tent, and summoned Aaron and Miriam. When the two of them came forward,
He said: "Listen to what I say: If there is a prophet among you from the Lord, I make Myself known to him in a vision; I speak with him in a dream.
References for Numbers 12:6
Not so with My servant Moses; he is faithful in all My household.
References for Numbers 12:7
I speak with him directly, openly, and not in riddles; he sees the form of the Lord. So why were you not afraid to speak against My servant Moses?"
References for Numbers 12:8