Sahih Bukhari
Fighting for the Cause of Allah (Jihaad)
Volume: 004 / Book Number: 052 / Hadith Number: 203
Narrated Ibn 'Umar:
The 'Prophet said, "It is obligatory for one to listen to and obey (the ruler's orders) unless these orders involve one disobedience (to Allah); but if an act of disobedience (to Allah) is imposed, he should not listen to or obey it."