How did people tell the difference between the prophet’s words and the revelation?

In Islam it is believed that the Quran is “the word of Allah”, meaning that it is given to the prophet word-by-word by the angel Jibril and the prophet transfered it to whomever was around him at the moment. However, not every word that the prophet spoke was a revelation. Sometimes it is the prophet himself speaking and sometimes it is the revelation. How did people know that they heard the Quran when the prophet spoke? Did the prophet specifically stated before and/or after he spoke that it was a revelation?