John Gill Commentary Numbers 12:6

"And he said, Hear now my words: if there be a prophet among you, I Jehovah will make myself known unto him in a vision, I will speak with him in a dream." — Numbers 12:6 (ASV)

And he said, hear now my words
The Targum of Jonathan reads, "I beseech you"; and Jarchi says, this particle always so signifies; but it is not so agreeable to the language of the divine Being:

if there be a prophet among you ;
not as making a doubt of it, but rather allowing that there was, and that there were others besides Moses, as even they themselves, Aaron and Miriam, and the seventy elders, and perhaps others; or at least there had been, and would be again, as there were in later times:

[I] the Lord will make myself known to him ;
that is, declare my mind and will concerning things present, or things to come:

in a vision ;
when awake, either by day or by night, representing objects to the bodily sight; as the almond tree rod, and the boiling pot, to Jeremiah, (Jeremiah 1:11–13) ; the visions of the chariots, (Ezekiel 23:24) (Ezekiel 26:7Ezekiel 26:10) , and dry bones, (Ezekiel 37:1–14) , to Ezekiel, and such as were shown to Amos, (Amos 7:1–9:15) : or to the mind by night, as if really discerned by the senses; as the visions of the man riding on a red horse, (Zechariah 1:8) , and of the four horns, (Zechariah 1:18) , and four carpenters, (Zechariah 1:20) , with several others shown to Zechariah:

[and] will speak unto him in a dream ;
as he had done to Jacob, (Genesis 31:11) , and as he did afterwards to Daniel, (Daniel 7:1) , and many others.