It is not for any believer, man or woman, when God and His Messenger have decreed a matter, to have the choice in the affair. Whosoever disobeys God and His Messenger has gone astray into manifest error (33:36).
...Those who believe in Our signs, those who follow the Messenger, the unlettered Prophet, whom they find written down with them in the Torah and the Gospel, enjoining the good and forbidding the evil, making lawful the good things and making unlawful the corrupt things, and relieving them of their loads and the fetters that were upon them. Those who believe in him and succor him and help him, and follow the light that has been sent down with him—they are the ones who prosper (7:156–57).
The Traditions declare:
• The best of words is the Book of God; the best way to follow is that of Muhammad. The worst affair is innovations (against my Sunna). Each innovation is a deviation. 
• "Everyone of my community will enter Paradise, except those who rebel." When they asked who these rebels were, he replied: "Whoever obeys me will enter Paradise; whoever disobeys me is a rebel." 
• In the case of my community, I am like someone who has lit a fire. Insects and butterflies flock to it. I hold you by the cloth [of your garments to keep you away from the fire], but you pull yourselves into it. 
• Don't let me find any of you seated in armchairs, who, when something I ordered or forbade is reported to them, respond: "We have no knowledge of it. So, we follow whatever we find in the Book of God." 
• Be careful! Surely I have been given the Book and its like together with it. 
• Those who outlive me will witness many controversies. Follow my way and that of the rightly guided successors (caliphs) who will guide to truth. Hold fast to it and cling to it stubbornly with your teeth. Refrain from newly invented things (in religion), for each such thing is an innovation, and each innovation is a deviation. 
• I have left to you two precious things that, if you hold fast to them, will never lead you astray: The Qur'an and the Sunna. 
 Bukhari, "I'tisam," 2.
 Muslim, "Fada'il," 17,18; Bukhari, "Riqaq," 26.
 Abu Dawud, "Sunna," 5; Ibn Ma'ja, "Muqaddima," 2; Tirmidhi, "'Ilm," 10.
 Abu Dawud, "Sunna," 5.
 Tirmidhi, "'Ilm," 16; Abu Dawud, "Sunna," 5; Ibn Ma'ja, "Muqaddima," 6.
 Imam Malik, Muwatta', "Qadar," 3.