Rashi: [One who has a dream] should tell it like folly, like other dreams, and establish it to be Nevu'ah.

Radak: How do you equate one who dreams a dream, and Nevu'ah that comes in a dream?! One who dreams, he tells his dream, and if it turns out that there is Emes in it, it is a little, for dreams are [based on] imagination [rooted it] thoughts while awake and thoughts of the future. Most are not correct - "va'Chalammos ha'Shav Yedaberu" (Zecharyah 10:2).

Malbim: A Navi knows the difference between a dream and Nevu'ah. If he knows that he has a dream, he tells that it is a dream, and not Nevu'ah. If he knows that it is My word, i.e. Nevu'ah, he says My true word, and does not mix in dreams and folly.

Radak: He will say something Emes. If it is My word in a dream to a Navi, he will say words of Emes without any Sheker at all. It says regarding dreams "Yesaper" and regarding Nevu'ah "Yedaber", for one who tells a dream, it is a mere story of what he saw, like one who tells things that he heard. The intellect has no share in it; it is through the power of imagination. It says about a prophetic dream "Yedaber", for it is via the power of Dibur, i.e. intellect, with the power of imagination.

Rashi: This is like Im ha'Bar - what does Sheker have to do with Emes?!

Radak: Words of dreamers are like straw. Its only benefit is for animals to eat it, or for work ¹ . Bar (grain) is for people to eat. How can one equate them?!

Radak citing Targum Yonasan: Like the difference between straw and grain, so is the difference between Resha'im and Tzadikim.

Radak citing Brachos 55a: Just like you cannot have grain without straw, you cannot have a dream without vain matters.

Malbim: This is one of the three ways to recognize whether something is Nevu'ah or a dream. (a) A prophetic dream has no mixture of straw or waste or anything false; it is pure grain and true matters. Also refer to 23:29:1:3, 23:29:3:2.