If God transmit messages to Muhamad in various ways, how does Muhamad know which messages goes where?

Question

Does the Quran contain all of Allah's revelations? (Sunni view)

This one says that not all of God's message is in Quran.

Some go to Quran. Other goes somewhere else.

How does Muhamad knows, oh, this message is in Quran. This one can go to Hadits?

Answer 1

First of all the given answers of the linked question don't seem satisfactory to me even if they provide enough information to already answer your question which seems to me based on a superficial reading.

The qur'an (and only the qur'an) is the revelation of Allah the almighty. Usually if Muhammad () got a new revelation he would call his scribes and dictate it to them. He would even tell them were to arrange it in the middle of the existing texts. See for example Prophet Muhammad SAW was illiterate, who wrote the Quran then? and also Is the Quran really preserved or are there missing parts of the Quran?.

Else the sunnah be it what we call hadith or hadith qudsi is related to the prophet () and his interpretation of the qur'an in the daily life and his knowledge about Allah the almighty. He neither would call any scribe nor ask people to write it down. So the sunnah consists of reports of what he said or did or confirmed (or didn't deny) beyond the qur'an.
Nevertheless it is interpreted as a kind of revelation based on a litteral interpretation of the verses:

Your companion [Muhammad] has not strayed, nor has he erred, (2)
Nor does he speak from [his own] inclination. (3)
It is not but a revelation revealed, (4) (53: 2-4)

Answer 2

I'm going to answer your question with a question that should be an answer to your inquiry.

Some memories that you yourself have, you know you've lived them in real life and were not a dream.

How do you know that these memories are memories of real events and not memories of dreams? You just know.

You may say that I can confirm with people, or with evidence in the environment. But there will still be some memories that you know have happened that you would not have anyone to confirm with or anything left in the environment as evidence. Yet you somehow know that they were real.

This does not mean that that's how Prophet Mohamed PBUH knew how distiguish. But it is to give an analogy that something of the like is very possible, in fact it is happening in your own self and you don't doubt it.

I hope this helps.

Cheers.