1204. Narrated Aboo Huraira (radhi Allaahu anhu) : Allaah’s Messenger (Sallallaahu Alaihi Wasallam) said,
Whoever obeys me, he obeys Allaah, and whoever disobeys me, he disobeys Allaah, and whoever obeys my ruler (the ruler I appoint) he obeys me, and whoever disobeys my (appointed) ruler, he disobeys me.
[Saheeh Al-Bukhaari, Hadeeth No. 251, Vol. 9]
Source : The Book Of Al-Imaara – Chapter 8 – It is obligatory to be obedient to the ruler except in sinful matters. Al-Lulu Wal-Marjan,Compiled by : Fuwad Abdul-Baqi,Translated by : Dr. Muhammad Muhsin Khan