We have sent down to you the book with truth, authenticating what is present of the book and superseding it. So judge between them by what God has sent down, and do not follow their desires from what has come to you of the truth. For each of you We have made laws, a structure. Had God willed, He would have made you all one nation, but He tests you with what He has given you, so advance the good deeds. To God you will return all of you, and He will inform you regarding that in which you dispute.
Translation endnotes
[5:48-50] Prophet Muhammed was not judging among people according to divine instructions besides the Quran. The Quran was the only divine authority. However, decades after Muhammed, those who turned away from the Quran turned Muhammed himself into a competing, supplementing, or contradicting authority through hadith collections and thereby regressed to the days of ignorance. The system belongs to God alone. Muhammed's sole mission was to deliver God's system to humanity. See 6:19, 112-116.