The word sunnah (plural sunan) is mentioned 16 times in the Quran. The concept of sunnah is used in two senses in the Quran:
Sunnah means the path or method followed (Ibn Manzur, Lisân al-ʿArab, headword S-N-N). Sunnah is the way that all prophets and therefore all believers must follow, that is, the way of revelation (wahy): “Allah wants to make clear for you, guide you to the ways (sunan سُنَنَ ) of those before you and accept your repentance…” (an-Nisa [4] 26).
The concept of sunnah of Allah in the Quran means the social laws of Him: “This is the law of Allah (sunnatillah سُنَّةِ اللّٰهِ ) that He applied to those before. You will not find any change in the law of Allah.” (al-Fath [48] 23. See also al-Ahzab [33] 38, 62; Al Imran [3] 137; al-Hijr [15] 13; al-Isra [17] 77; al-Ghafir [40] 85). Example of Sunnah of Allah: If those who disbelieve repent, their past deeds will be forgiven. If they return again, they will go to hell (al-Anfal [8] 38. Also Fatir [35] 43; al-Kahf [18] 55).
As a result, the sunnah mentioned in the Quran, is the way of revelation (wahy) that every Believer must follow and the unchangeable social practices and prohibitions for societies.