Islam gives full recognition to two basic realities of human existence: 1) Exercise of some authority or power by some individuals over others is necessary to create and maintain order and progress in the society (4:59, 43:32). 2) It is easy for power to get corrupted and become a source of injustice, oppression, and stagnation (6:123, 20:24, 27:34, 33:67, 34:34, 43:23-24 etc). In what follows I briefly outline in broad terms the way Islam deals with these two realities, concentrating mostly on the theory derived from Islam’s primary source – the Qur’an.
In general, there are two ways in which Islam aims to control the tendency of power towards corruption. First, it reforms the concept of power itself by depriving human authority of absolute basis of every type, making it accountable, and defining its function. Second, it empowers the people to oppose corrupt power.
The starting point for the Islamic conception of human power and authority is the declaration: la ilah illa allah (there is no god but the one true God). The Qur’an often relates this declaration, which is the first part of the basic Islamic confession of faith, with the statement that power and authority resides only in God (2:165, 5:17, 12:40, 13:31 etc). This means that no human being can legitimately exercise any power or authority over any other human being except as a servant of God.
Often corrupt power and authority uses religion itself to install and perpetuate itself. Islam has some safeguard against this in the principle that there are no intermediaries between God and human beings. There are no ordained priests. Everyone can lead the prayers and perform religious ceremonies. The Qur’an explicitly rejects the idea that human beings need the mediation of any beings other than God to bring them closer to God: Is it not to God that wholehearted devotion is due? But those who take protectors other than God (say): “We worship them so that they may bring us nearer to God”… (39:3).
The messengers of God do, of course, exercise divinely sanctioned authority but they simply call people to God and help them by their teaching and example to build a relationship with God. In Islam they do not act as intermediaries between God and the people. Indeed, their true mission is to enable human beings to have an independent relationship with God without any intermediaries.
Oppressive power is also often sustained by perpetuating established ideas and traditions which are given a nearly absolute validity. The Qur’an rejects this attitude: And when it is said to them, "Follow what God has sent down," they say, "Nay, we would rather follow what we saw our fathers following". What! Even if their fathers did not understand anything and were not rightly guided? (2:170, also 5:77, 104, 31:21, 43:22-24). However, the Qur'an is not rejecting here past traditions just because they are past traditions or just because they are man-made. It simply wants people to critically judge what their forefathers have passed on to them. The followers of the Qur'an are neither compulsive rebels against traditions, nor their uncritical slaves. Indeed, the main cause of all human problems is either the tendency to slavish adherence to the past authorities or to compulsively rebel against them. The Qur’an rejects both extremes.
The Qur’an further teaches that legitimate human power and authority exists for one and only one function: to "establish regular prayers and practice regular charity and enjoin the right and forbid the wrong..." (22:41). It is significant that the words for right and wrong (ma`ruf and munkar) refer in the first place to what is universally approved or disproved by human nature when it has not been perverted. Religion itself is viewed in the Qur’an as the religion of the true (uncorrupted) nature (fitrah) of man, a knowledge of which is ingrained in human beings (30:30-31, 91:7-10, 95:4-8). Prophets and messengers of God manifest this fitrah of man and revelation is nothing but such manifestation.
Finally, since no human being has an inherent right to exercise authority over others, all human authority is held accountable. In the Qur’an there is a great emphasis on the accountability of all human actions, including, of course, those related to the exercise of power and authority.
All the above principles apply to all individuals without exception, even to the messengers of God. The authority that the messengers exercise “by God’s leave” (4:64) derives from their being servants of God who manifest the fitrah of man and safeguard it against deviations, to which human beings are highly prone. They are completely human and have no inherent right to any power. They, like other human beings are accountable, even they would stand before God and account for what they did with their divinely appointed mission (5:112-113). Also, they exercise their authority only over those who have freely accepted it (2:256), although those who reject this authority do so by deviating from their own true nature and would reap the consequences of such rejection.
The need for messengers arises because the tendency for power and authority to get corrupted is ultimately related with the tendency towards corruption in all of us. Hence there is need for some persons to arise who have not only themselves overcome this tendency for corruption but are also able to shine as an example for others. Muslims are those who have accepted Muhammad as such a figure, a fact that finds expression in the second part of the Islamic confession: muhammad ar-rasul allah (Muhammad is the messenger of God).
Messengers are almost always raised from among the relatively weak sections of the society. This is true, for example, of the three of the major prophets: Moses, Jesus and Muhammad. Moses was raised from among the downtrodden Israelite slave community of Egypt. Jesus was raised from among the Jewish nation under Roman occupation, and even in the Jewish nation he belonged not to the rich and powerful but to the peasant community in a little known village in Galilee. (The gospel tradition affirms Jesus’ royal lineage, but the Qur’an does not mention this tradition.) And Muhammad was born as a poor orphan. Although, assured of final victory the messengers are almost always opposed by the rich and powerful (6:34, 112, 123, 14:13, 25:31, 34:34 etc) who expect that if there has to be a messenger from God it should be from among them (43:31).
Sometimes God himself intervenes to dislodge a corrupt power, first by sending a messenger as a warner and then by the destruction of the powerful if the message is not heeded. This happened in a most clear way in the case of Pharaoh, but every prophet and messenger of God in fact necessarily gets involved in an opposition with some corrupt and established powers and dislodges them, sometimes during his lifetime (as in case of Moses and Muhammad) and sometimes after his departure (as in case of Jesus).
But since Muhammad is the last of the prophets of God, the Qur’an ensures opposition to power’s tendencies to corruption by empowering the only source from which challenge to power can come without a direct divine intervention through a messenger: the people. The Prophet did not appoint any person as his successor because after his departure his function passes on not to any particular individual but to the whole community of believers. Thus in his life he was a “witness” while after him the role of witnessing passes on to the community as a whole (2:143, 22:78). The task of enjoining right (ma’ruf) and prohibiting wrong (munkar) is not left in the Qur’an to individuals in authority, but is given to the whole community: "Believing men and believing women are protecting friends of one another; they enjoin what is right and forbid what is wrong; they establish regular prayer and regular charity ..." (9:71, see also 3:104, 9:112, 31:17). A well-known hadith also states this in clear terms: "If one of you sees something wrong, let him change it with his hand; if he cannot, then with his tongue; if he cannot, then with his heart and this is the weakest faith." Some versions add: "there is no part of faith behind that, not even so much as a mustard seed." The Qur’an does not recognize any attempt to justify one’s conduct by blaming the powerful or the previous generations; each person is obligated to stand for what is right to the best of his or her abilities (7:38-39, 33:67-68).
Further empowerment of the people is found in verses where it is from among the people that some are expected to rise up and check others who may spread corruption in the land: “If God had not defended people some against others corruption would have spread over the earth; but God is bountiful to all the worlds (2:251). If God had not defended people some against others, monasteries, churches, synagogues and mosques in which God’s name is remembered much, would have been destroyed (22:40; see also 49:9-10).
Yet another way in which the Qur’an empowers the people is the principle of mutual consultation: (believers are those whose "affairs are conducted by consultation among them" (42:38; see also 3:159).
 All references are to the Holy Qur’an.