Allah, the Wise, has said:
وَ سَيَعْلَمُونَ الَّذِينَ ظَلَمُوا أَيَّ مُنقَلَبٍ يَتقَلِبُونَ
"And they who act unjustly shall know to what final place of turning they shall turn back." 
Imam Baqir (a.s) said:
مَا مِنْ أََحَدٍ يَظْلِمُ بِمَظلِمَةٍ إِلاَّ أََخَذَهُ اللهُ تَعاَلـى بِهَا فِي نَفْسِهِ أََوْ مَالِهِ.
"There is none who commits oppression by means of an (act of) injustice, except that Allah afflicts him or his wealth because of it." 
Oppression and injustice are, in reality, insubordination to the orders of Allah, acts of transgression and a consequence of transcending the limits of the Shari'ah and the intellect.
All throughout history that which has befallen the weak and the oppressed has been due to the oppression of the oppressors. Power and craving for dominance serve as a prelude for a disobedient soul to oppress the vulnerable and weak individuals.
One who transgresses the Divine limits and is uninhibited with respect to every kind of oppression and injustice such as murder, Abuse, vilification, fornication, rape, usurpation of the property of others, etc… has, in effect, gone out of the bounds of Allah's obedience, drowned himself in carnal desires and become afflicted with the disease of rebelliousness. Such a person, sooner or later, shall be seized by punishment and retribution, since the lamentations of the weak, oppressed and the orphaned ones possess negative overtones, which manifest themselves in this world and the hereafter.
1 – The Oppression of Dadhanah
In Syria. there lived a king by the name of Dadhanah, who was an idol worshipper. Allah sent Prophet Jorjis (a.s) to Dadhanah to advise him and invite him to monotheism, but instead, Dadhanah responded by asking him: "Which city do you come from?" He (a.s) replied: "I am of Roman origin and have come from Palestine."
Upon Dadhanah's orders, Prophet Jorjis (a.s) was imprisoned, his holy body subjected to injuries by means of iron spikes till his flesh fell apart and vinegar poured over the wounds. After this, his thighs, knees, soles of his feet and head were pounded by means of red-hot iron skewers to such an extent that he was on the verge of death.
Allah sent an angel to him (a.s), who said: "Allah says: 'Be patient and happy, and fear not for I am with you and shall deliver you from them. They shall attempt to kill you four times, but I shall ward away the pain and agony of the sufferings from you.'"
The second time Dadhanah ordered that this Prophet's back and stomach should be lashed after which he should be hurled into prison. He then summoned every sorcerer and magician before him and ordered them to use their magic to his benefit against Prophet Jorjis (a.s), but despite their best efforts, their magic failed to have any effect upon him. Having failed in this, they tried to poison him, but Prophet Jorjis (a.s) recited Allah's name and the poison caused him no harm.
One of the magicians said: "Had I fed this poison to all of the inhabitants of the earth, they would have turned blind, their appearances would have changed and all of them would have perished!" Then, repenting over his past misdeeds, he declared his faith in Prophet Jorjis (a.s), whereupon Dadhanah had him killed.
For the umptinth time Dadhanah hurled Prophet Jorjis (a.s) into prison and on this occasion ordered his body to be cut into pieces and thrown into a well.
With the objective of admonishing him, Allah sent down lightening and earthquake, but he refused to heed the warning. Allah sent the angel Mikail, who brought Prophet Jorjis (a.s) out of the well and said to him: "Be Patient," and then conveyed to him glad tidings of the divine rewards.
(Once again), Prophet Jorjis (a.s) approached the king and invited him towards monotheism, but once again he refused. However, on this occasion, the commander of his army together with four thousand people brought faith. Witnessing this, Dadhanah ordered all of them to be put to death.
This time he prepared a tablet out of molten copper and forced Prophet Jorjis (a.s) to lie upon it. He then poured molten lead down his throat and then, lighting up an inferno, hurled him into it in order that he be burnt to death.
This time too, Allah sent Mikail to grant him soundness of health. Having regained his health, Prophet Jorjis (a.s) approaching the king yet again advised him to abandon idolatry and invited him towards monotheism.
On this occasion, Dadhanah hurled him into a cauldron containing molten lead and sulphur, and ignited a fire under him in order to melt his body with the molten lead and sulphur. Allah sent down the angel Israfil, who issued a shriek causing the cauldron to topple over and leaving Prophet Jorjis (a.s) safe and unharmed.
Having regained his health by the power of Allah, he (a.s) again approached Dadhanah and invited him towards Allah-worship. Frustrated and desperate, Dadhanah ordered all the people to gather together in the desert and kill him in unison, whereupon Prophet Jorjis (a.s) supplicated to Allah and pleaded for patience and fortitude.
The people beheaded him (a.s) and were on their way back when all of them were seized by an onslaught of Divine chastisement.
2 – Working for the Oppressors
A person, by the name of Muhajir, narrates as follows: "I had gone to Imam Sadiq (a.s) and said to him: "Such and such persons have sent you their salutations." The Imam (a.s) responded in kind, whereupon I said: "They have also requested you to pray for them." He (a.s) inquired: "What is their problem?" I said: "Mansur Dawaniqi has flung them into prison."
He (a.s) asked: "What did they have to do with Mansur (that he hurled them into prison)?"
I replied: "They used to work for him and one day, in a fit of anger, he hurled them behind bars."
The Imam (a.s) said: "But had I not prohibited them from working for him (an oppressive and unjust regime)? Such work entails great danger." Having said this, the Imam (a.s) then prayed: "O' Allah! Repel from them the evils and grant them deliverance."
Muhajir says: "I returned from Mecca and inquired about my friends whereupon I was informed that they had been set free"" - (according to the dates, they had been released three days after the Imam (a.s) had prayed for them).
3 – Retaliation
Once, Hadhrat Musa (a.s) was passing by a region when he came across a spring which flowed alongside a mountain. Performing ablution with the water, he proceeded to the top of the mountain to offer prayers. Meanwhile a person on horseback reached the spring and came down from the horse with the intention of quenching his thirst. When he had satiated himself he mounted his mount and galloped away, dropping his money-pouch in the process.
A short while later a shepherd arrived there; noticing the money-pouch, he picked it up and left.
After the shepherd had left, an old man - a bundle of fire-wood on his head and possessing an appearance that manifested his destitution and poverty - reached there. Placing his load on the ground he stretched himself out near the spring and went to sleep. Before long the rider returned to the spring and began searching for his lost money-pouch. Failing to locate it, he questioned the old man, who pleaded ignorance about it. There ensued an altercation betwin the two and very soon they began trading blows. In the resulting brawl, the rider beat the old man so severely that he died.
Witnessing this, Prophet Musa (a.s) said: "O' Lord! What kind of incident was this and what kind of justice exists in this episode; the money was taken by the shepherd but it was the old man who had to face oppression and injustice?"
He (a.s) was told: "O' Musa! This old man had killed the rider's father and so retaliation was achieved between them. (In addition) the rider's father had owed to the shepherd's father, the same amount that was contained in the money-pouch and in this way, the shepherd acquired his right. O' Musa! (Do know) I pass My judgment on the basis of justice and fairness."
4 – The Oppression of Dhahhak Himyari
Having ruled Iran for years, Jamshed slowly came to be filled by pride, ultimately claiming Allah-ship for himself and inviting the people to worship him. The people, out of fear of his sword, submitted to his demand; this continued till Dhahhak initiated a military expedition against him and eventually killed him.
Placing himself at the helm of affairs of the sultanate, Dhahhak adopted a policy of oppression and persecution - killing his father and subjecting his people to various forms of brutality and tribulation.
One day he happened to experience discomfort in his head and shoulders. One evil cook suggested a remedy saying: "The thing that can cure you is the brains of the youths."
Upon Dhahhak's orders two youths from the prison were killed; eating their brains, he felt slight comfort in his state and so went to sleep. Next day onwards two youths would be killed everyday and their brains utilized for his treatment.
He committed great brutalities, never gave ear to any petition and never meted out justice to any oppressed and so, when he murdered two sons of Kaveh, the ironsmith, it turned out to be the final straw and provoked a rebellion against him.
He was ultimately killed in an extremely gruesome manner - his head bludgeoned by a mace (or hurled into the depths of a well, according to another report), and it was Faridoon, who later took over the reins of the sultanate.
5 – The Incident of Harrah
After the incident of 'ashura and two and a half months before his death, Yazid initiated yet another horrendous act on the twenty eighth of Dhul Hijjah of the year 63 ah - the looting and killing of the people of Madinah and sacrilege with respect to the shrine of the Noble Prophet (s.a.w) at the hands of an old, sick, brash and impudent man by the name of Muslim Ibn 'Aqabah, notoriously known as Musrif.
When the news of Yazid's oppression and depravity reached the ears of the people of Madinah, a group from amongst them proceeded to Syria to obtain first-hand information regarding the situation.
Witnessing his sacrilegious behaviour, they returned to Madinah and drove his governor, 'Uthman Ibn Muhammad, together with Marwan Ibn Hakam and the other Umayyads, out of the city. The people then flocked to 'Abdullah Ibn Handhalah - the 'Ghasil al-Malaikah,) and pledged allegiance to him. Coming to know of this, Yazid dispatched a force under the command of Musrif towards Madinah.
In order to defend themselves, the people of Madinah came out of the city and took up positions in a region known as Sangistan, where a fierce battle ensued betwin the two forces. Some of the inhabitants of Madinah were killed while others fled and sought shelter in the holy shrine of the Noble Prophet (s.a.w).
Musrif's soldiers advanced into Madinah, entered the holy shrine on horseback and began their carnage - killing so many people that the mosque and the holy tomb were covered with blood; the number of people that were killed have been reported to be around eleven thousand!
We state one example of the numerous brutalities committed by the forces of Musrif: One of the soldiers of the army of Yazid, an inhabitant of Egypt, entering the house of a lady from the Ansar (The Helpers), who had recently given birth to a child and which was in her arms, said to her: "Bring me all your wealth." The lady said: "By Allah! They have not left behind anything that I can give you." (Hearing this) he said: "I shall kill you and your child." The lady pleaded: "Fear Allah, for this infant is the child of Ibn Abi Kabshah Ansari, the companion of the Noble Prophet (s.a.w)." The name seemed to have no effect upon the merciless man, who, picking up the innocent child by its legs - even as it was being suckled, flung him against the wall scattering his brains upon the floor.
In the face of such atrocities, all the people of Madinah were forced to pledge allegiance to Yazid, with the exception of two persons - Imam Zainul 'Abidin (a.s) and Ali Ibn 'Abdullah Ibn Abbas.
The Imam (a.s) arrived before Musrif after reciting a supplication as a result of which he was so was overcome with dread and awe that he could not get himself to kill the Imam (a.s). As for Ali Ibn 'Abdullah, some of his maternal relatives were present in Musrif's army and they prevented him from being killed.
 Suratul Shua~ra (26), Verse 227
 Jami~ al-Sa~adat, vol. 2, pg. 220
 Ihya al-Qulub, pg. 76
 Hayat al-Qulub, vol. 1, pg. 477
 Shanidaniha-e-Tarikh, pg. 57; Mahajjah al-Baidha, vol. 3, pg. 256
 Pand-e-Tarikh, vol. 3, pg. 161; Shaytan, vol. 2, pg. 424
 Jawame’ al-Hikayat, pg. 52
 One, whose ablution (ghusl) has been performed by the angels. (Tr.
 Madayani reports that in the aftermath of the incident of Harrah thousands of unwed maidens gave birth to illegitimate children, who were referred to as ‘aulad al-Harrah’ (children of Harrah) - a consequence of the transgressions committed by Musrif’s soldiers with the maidens and women of Medinah. Tatimmah al-Muntaha, pg. 39
 The incident of Harrah has been reported, in addition to Shiite sources, by the Sunnite sources as well, such as Kamil (of Ibn Kathir), Maqatil al-Talibeen, Kashf al-Astar, Al-Imamah Wa al-Siyasah, Akhbar al-Duwal, Tarikh Masu’di.
 Muntahal A~mal, vol. 2, pg. 34