Fighting for the Cause of Allah (Jihaad)
Bukhari :: Book 4 :: Volume 52 :: Hadith 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."