And obey Allah and the Messenger; that ye may obtain mercy. (Surah Aal Imraan, Verse 132)
The Ayaah clearly differentiates the two sets of commandments. The word and in the ayaah clearly denotes that the commands of the Messenger, which we are supposed to obey, are seperate from the commands of Allah, which is the Quran.
Now what is this set of commands or teachings that Allah has commanded us to obey, in the latter part of the Ayah? It clearly cant be the Quran itself, because they have been seperated by an "and".
But remember the goodness which God has shown you and how much of the Book and the Wisdom He has sent down to you to admonish you thereby [Q. II, 231].
Shafi said the wisdom is the Sunnah and seperated the two with the "and" you said. However the verb the Quran uses:
وَاذْكُرُوا نِعْمَتَ اللَّهِ عَلَيْكُمْ وَمَا أَنزَلَ عَلَيْكُم مِّنَ الْكِتَابِ وَالْحِكْمَةِ يَعِظُكُم بِهِ ۚ وَاتَّقُوا اللَّهَ وَاعْلَمُوا أَنَّ اللَّهَ بِكُلِّ شَيْءٍ عَلِيمٌ
is a singular verb and not a plural verb. Meaning the Quran sees it as one. Also the Quran says"
And call to mind the signs of God and the Wisdom which are recited in your houses; verily God is gentle, well-informed [Q. XXXIII, 34].
Its hard to see how recite here can mean anything other than the Quran. So we then have :
4.59 O ye who believe! Obey Allah, and obey the Messenger, and those charged with authority among you. If ye differ in anything among yourselves, refer it to Allah and His Messenger, if ye do believe in Allah and the Last Day: That is best, and most suitable for final determination.
So we have to be somewhat careful as to what the Quran is saying because here its using obedience in a general way. But this is also concerning those who were there at the time of the prophet since they were there to hear him and listen to him and he was there to talk to them and deal with them. But when we are talking about after his death, its another matter since we have the Quran and the Quran never gave us any commands to deal with anything outside it except the previous scriptures. So we must take that command of obedience in a general way. Remember not all Quranist reject hadith outright, many just don't accept it the way the sects do. We will never know what truly happened and we know from the Quran that the hypocrites were spreading lies and rumours when the prophet was still alive so imagine after 150 years. But most of all we must never accept any binding commands not addressed in the Quran and we should not accept what contradict the Quran. I am sure there are many hadiths that are true and reflect truths, but there are many that were placed for theocratic and orthodoxy reasons and many contradict the Quran.
Many hadiths preach righteousness and heavenly works, but many don't and preach hate and violence. So I don't take things like the sects do. But to try to rely on general verses like "obey the messenger" is dangerous. The Quran uses language variably and is often difficult to speculate on their meanings. None of us here take the command to obey those in charge of authority over us in the same way we take a prophet or a messenger.
Plus there is no reason to believe that the prophet dealt with matters and talked about matters seperate from the Quran, at least not in concept. The Quran says:
"Surely We have revealed the Book to you with the truth that you may judge between people by means of that which Allah has shown you; and be not an advocate on behalf of the treacherous." (4:105)
"And We have revealed to you the Book with the truth, verifying what is before it of the Book and a guardian over it, therefore judge between them by what Allah has revealed, and do not follow their low desires (to turn away) from the truth that has come to you;" (5:48)
"Allah is witness between you and me; and this Quran has been revealed to me that with it I may warn you and whomsoever it reaches." (6:19)
"We know best what they say, and you are not one to compel them; therefore remind him by means of the Quran who fears My Promise." (50:45)
Of course what God has revealed and shown the prophet is a very broad thing but we must not assume that is could be radically different than the Quran. At least the Quran has the essential aspects of what God revealed to his prophet and what mankind needs to know. I am not saying that all hadiths should be thrown away, but the way the sects have used them and the things they claim is from the prophet can not be so because it contradicts the Quran and it adds to the deen many things the Quran never said. This is a very complicated topic and there will be more debates about this in the future.
Shafi's problem is he over streches the verses of the Quran and this is dangerous. Christians do the same with the Gospel and this leads to taking things out of context.