THE SUNNAH IS (Wahy) REVELATION FROM Allah
Shaykh Saalih Aal Shaykh Hafidhaullaah said in his explanation of ‘The Superiority of Islam’:
And the Sunnah is the sister of the Qur’an in that it is a revelation from Allah. And that the Sunnah is an explanation of the Qur’an and it expounds (in detail) on its (the Qur’an’s) rulings. It is from Allah.
Indeed Hassaan ibn ‘Atiyah rahimahullaah used to say: “Jibreel used to descend upon the Prophet sallallaahu alayhi wa sallam with the Sunnah just like he used to descend upon him with the Qur’an.”
Also it is authentically reported from him sallallaahu alayhi wa sallam that he said:
“Verily I have been given the Qur’an and it’s like with it.”
And Allah azza wa jall said:
“Allah has sent down to you the Book and Al-Hikmah, and taught you that which you knew not. And Ever Great is the Grace of Allah unto you (O Muhammad sallallaahu alayhi wa sallam).” [An-Nisa:113]
And Al-Hikmah (mentioned in the verse) is the Sunnah. So the command of the Prophet sallallaahu alayhi wa sallam is a command from Allah azza wa jall.
Source: The Superiority of Islam, by: Shaykh-ul Islam Muhammad Ibn Abdul Wahhaab – Explained by: Shaykh Saalih Aal Shaykh – page: 236.