A man asked the Prophet, peace be upon him,
‘What kind of jihad is better?’ He replied, ‘A word of truth in front of an oppressive ruler.’
(Sunan Al-Nasa’i , No. 4209)
Narrated Ma’qil: I heard the Prophet (peace be upon him) saying:
"Any man whom Allah has given the authority of ruling some people and he does not look after them in an honest manner, will never feel even the smell of Paradise."
Sahih Muslim - Volume 9, Book 89, Number 264.