Allah'S Protection Of Quran
Not necessarily. E.g. Circumcision is considered a Sunnah, although it is not mentioned in Quran. It is considered a recommended practice for a better hygiene, although not directly a part of religion as it is not a divine commandment. Sometimes contours of a ritual are given in Quran, and in addition to that an established practice received through perpetual transmission makes it easier to perform it. For instance, in Salat, the order of Qiyam, Ruku, and Sujud is taken from Sunnah which helps to standardize it, otherwise everyone would be performing salat differently and there would be no uniformity. In the case of fasting, almost all the details are given in Quran, so no other substantial information is required from Sunnah.