So, if we follow the Sunnah, then we're following in obedience4. And obedience isintelligence, Therefor, obedience is also the light. So they follow the Prophet (pbuh) and the light that came down with him right? And these are two different ones the Light is the Guidance of G'd and the Prophet (pbuh) is his Uswatan Hasana. So, the excellence of the Prophet (pbuh) is what we follow. They say, Sunnah I don't like the term Sunnah, we use it too much we should just say followthe Prophet (pbuh), that's enough.In the Qur'an Allah doesn't say follow The Prophet’s (pbuh) Sunnah, it says follow him.
But now because of the Shiite there is a need for one side to say this is how to perceive the Prophet. So they start using the term Sunnah to say this is how we perceive him.
And in this way they establish what is Sunnah.
In the time of the Prophet (pbuh) what established what was the Prophet (pbuh) was hisrole as a Messenger of G'd and his character.