Bamidbar/Numbers 12:6 is often translated as something like “when a prophet of the Lord arises among you…” However, both Robert Alter and Everett Fox note in their translations — see Source Materials — that the Hebrew here is difficult.
Fox renders the “awkward” Hebrew as: “If there should be among-you-a-prophet of YHVH….”
Alter says the “cryptic” Hebrew literally reads: “If-there-be your-prophet the-Lord.” He notes that the call to “hear” [shimu-na] is “one of the conventions for beginning a biblical poem,” and translates this passage as follows:
Listen, pray, to My words.
If your prophet be the LORD’s
in a vision to him would I be known,
in a dream would I speak through him.
Not so My servant Moses,
in all my house is he trusted.
Mouth to mouth do I speak with him,
and vision, and not in riddles,
and the likeness of the LORD he beholds.
And why did you not fear
to speak against My servant Moses?