You should rule among them by what God has sent down, and do not follow their wishes, and beware lest they divert you away from some of what God has sent down to you. If they turn away, then know that God wants to inflict them with some of their sins. Indeed, many among the people are corrupt.
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.