The Messenger of Allah (s) said during his lifetime: “Whoever observes a ruler (sultan) legalizing what Allah has made unlawful, violating the covenant of Allah, opposing the Sunnah of the Messenger of Allah, and treating the creation of Allah sinfully and oppressively, and does not oppose him with his speech and action, Allah has a right to bring him to the same fate as that of the tyrant’s” (narrated by Imam Husain (AS), attributed in ‘Allama Majlis, Bihar al-Anwar, v. 44, p.381)

O’ Zurarah! The sky had cried for forty days over Husain (A.S.) (Imam Jafer Sadiq (AS) Mustadrakal Wasail, vol 1 pg. 391

Allah revealed to Jesus : ‘O, Jesus , it is (obligatory) upon you to follow the path of the predecessors, so that you join the group of the Prophets. O, brothers of the warners, tell your people not to enter any of my houses except with pure hearts, clean hands and humbled eyes. For verily, I do not hear the prayers of a supplicant who has usurped the right of any of my servants, nor do I answer the prayers of the one who owes me an unfulfilled duty.’ (as narrated by Imam Ali (AS) attributed in al-amali, ch. 16, #1)

In Al-Irshad it is narrated that Imam Sadiq (a.s) said: “Allah the Almighty is not similar to anything, and nothing is similar to Him. He is different from whatever we can imagine.” (attributed in mishkat al-anwar, #12)

Masaedat ibn Sadaqih said that Imam Sadiq (a.s) was questioned about the Prophet’s statement: “The best form of Jihad is expressing what is just in the presence of an oppressive ruler.” Imam Sadiq (a.s) said: “This act will only be accepted of him if his enjoining the right is based on knowledge, otherwise it is not accepted.” (as narrated in Mishkat al-Anwar, ch. 13, #241)

see also: jihad, resistance, just war, and terrorism.

“Now, the rulers have introduced evil acts of which we did not know; discarding the Tradition of the Prophet and introducing the innovations. A truthful person is held a liar, generosity is displayed without fear of Allah and a trustworthy from among the righteous people is deprived. O Allah! If you have destined good for me, then take me away into Your proximity, without having changed.” ( Abu Dharr al-Ghifari - may Allah bless him with mercy - attributed in Al-Amail, ch. 14 #5)

O Kumail, dividend from wealth disappears with its loss, O Kumail, the hoarders of wealth have died, while the learned exist for ever; their bodies have disappeared but their teachings and wisdom are ingrained in the hearts. (Imam Ali (AS) attributed in Al-Amail, ch. 29, #3)