The Muslims during the days of Prophet Muhammad lived by the sharī‘a by following the Qur’ān and the Sunna. Sunna means the example of the Prophet. (Sunna is sometimes written as ‘sunnat’.)
Was not the Qur\’ān enough on its own? The Qur\’ān is a book of guidance which was sent for the entire human world till the end of time. As such, it only deals with the general issues and mentions only the basic principles underlying the Muslim way of life. The Qur\’ān is more like a constitution than a book of law. The deals were left to the Prophet.