asalamualaikum how did the companion of prophet muhammad known if his teaching is the speech of the holy quran or his hadith?

All Perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as that of his family and all his companions.

Without a doubt, both the Quran and the Sunnah were revealed by Allaah. Allaah Says (which means): {Nor does he speak from [his own] inclination. It is not but a revelation revealed}[Quran 53:3-4].

However, the Companions used to differentiate between the Quran and the Sunnah in accordance with the instruction of the Prophet to them. Imaams Ahmad, At-Tirmithi, An-Nasaa'ee, Al-Bayhaqi and Al-Haakim, in His Mustadrak reported that ‘Uthmaan said: "When the verses of the Quran were revealed to the Prophet he called someone to write them down for him and said to him: ‘Put this verse in the chapter in which such and such has been mentioned;’ and when any verses were revealed, he used to say (similarly): ‘Put this verse in the chapter in which such and such has been mentioned’ …. ".

Furthermore, it was authentically reported from the Prophet that in the initial phase of revelation, he encouraged his companions to write down the Quran only lest it gets mixed with the Hadeeth. Imaam Ahmad reported in his Musnad that Abu Hurayrah said: "We were sitting and recording what was the Prophet was saying. The Prophet came out and enquired, "What are you writing?" we said, '(we are writing down) what we hear from you.' He said: "Is there a book along with the Book of Allaah?" we said, '(we write) only what we hear from you. He then said: "Write down the Book of Allaah only, do not mix the Book of Allaah with any other thing.  Is there any book along with the Book of Allaah? Write down only the Book of Allaah without mixing it with any other writing." The narrator said: 'we gathered all what we had written at a plane land and then we put it on fire. Then we asked, ‘O Prophet of Allaah! Can we narrate from you?' He replied, “Yes, narrate from me, there is no harm, but whoever intentionally tells a lie on my behalf, let him prepare himself to occupy a seat in Hell-Fire…."