Theological Basis of Islamic State

From: http://www.islamic-world.net/islamic-state/theobasis.htm

Khilafah is fard - Evidence from the Quran

The evidence that the appointment of a Khalifah is obligatory upon all Muslims is in the Quran, Sunnah and the Ijma' (consensus) of the Sahabah.

Evidence 1
"And rule between them by that which Allah revealed to you, and do not follow their vain desires away from the truth which came to you". [TMQ 5:48]
Allah (swt) has ordered the Prophet to rule between Muslims by that which He (swt) revealed to him and has obliged Muslims to restrict themselves to all the rules of the Shari’ah. An order of Allah (swt) to the Prophet is an order to the entire Ummah, unless there is evidence which limits the order to him. In this case there is no such evidence, so the order to rule by all that Allah has revealed is binding for all the Muslims.
Because the word Ma (what) is general in its meaning, it signifies that the order refers to all of the aspects of governing that have been revealed, and not merely a part of it.
This order to the prophet has been given in a decisive manner, and does not leave room for doubt or alternative meanings or understandings.

Evidence 2
"..Verily the 'Hukm' (command, Judgment) is for none but Allah.." [TMQ 12:40]
This ayah states that the privilege of rule is reserved for Allah alone. In fact, it is an aspect of tauhid to refer to Allah for solutions to all of life’s affairs, and one of the names of Allah is "The Legislator".

Evidence 3
"Whoever does not judge by that which Allah has revealed, they are disbelievers" [TMQ 5:44]
"Whosoever does not judge by that which Allah has revealed, such are oppressors" [5:45]
"Whosoever does not judge by that which Allah has revealed, such are transgressors" [5:47]
Whoever does not govern with what Allah has revealed is of the disbelievers, or oppressors, or transgressors. Again, because the word Ma (what) in this verse is general, so it includes everything that Allah has revealed.

The Islamic System
Khilafah is fard - Evidence from the Sunnah
Evidence 1
On the authority of Muslim Nafi'a reported saying: "Umar said to me that he heard the Prophet saying: Whoso takes off his hand from allegiance to Allah (swt) will meet Him (swt) on the Day of Resurrection without having any proof for him, and whoso dies whilst there was no bay'ah (allegiance or a pledge) on his neck (to a Khaleefah), he dies a death of jahiliyyah."
The Prophet made it compulsory upon every Muslim to have a bay'ah on his neck, and described that whoever dies without a bay'ah on his neck dies a death of jahiliyyah. This does not mean that he dies as a kafir, rather, it means that he dies as if Islam had never reached him.
The bay'ah cannot be for anyone except the Khaleefah, and the Prophet made it obligatory upon every Muslim to have on his neck a bay'ah to a Khaleefah.
The Prophet did not make it an obligation upon every Muslim to give bay'ah to a Khaleefah. The duty is the existence of a bay'ah on the neck of every eligible Muslim, i.e. the existence of a Khaleefah who accordingly deserves a bay'ah upon the neck of every Muslim. So it is the presence of the Khaleefah which places a bay'ah on the neck of every Muslim, whether the Muslim gave a bay'ah to him in person or not, as silence signifies acceptance of the bay'ah from the Ummah.
Therefore, this hadith of the Prophet is an evidence that the appointment of the Khaleefah is an obligation and not a proof that giving the bay'ah is obligatory. This is so because the Prophet rebuked the Muslim who has not a bay'ah on his neck until he dies, not the one who did not give
Evidences 2-5
Hisham ibn 'Urwa reported on the authority of Abu Saleh on the authority of Abu Hurairah that the Prophet said: "Leaders will take charge of you after me, where the pious (one) will lead you with his piety and the impious (one) with his impiety, so listen to them and obey them in everything which conforms with the truth. If they act rightly it is for your credit, and if they acted wrongly it is counted for you and against them."
Muslim narrated on the authority of al-A'araj, on the authority of Abu Hurairah, that the Prophet said: "Behold, the Imam is but a shield from behind whom the people fight and by whom they protect themselves."
Muslim reported on the authority of Abu Hazim, who said: "I accompanied Abu Hurairah for five years and heard him talking of the Prophet's saying: The Prophets ruled over the children of Israel, whenever a Prophet died another Prophet succeeded him, but there will be no Prophet after me. There will be Khulafa'a and they will number many. They asked: What then do you order us? He said: Fulfill the bay'ah to them one after the other and give them their due. Surely Allah will ask them about what He entrusted them with."
Ibn 'Abbas narrated that the Prophet said: "If anyone sees in his Amir something that displeases him let him remain patient, for behold, he who separates himself from the sultan (authority of Islam) by even so much as a hand span and dies thereupon, has died a death of the days of jahiliyyah".
In these alhadith, the Prophet informs us that leaders will run the affairs of Muslims, and the alhadith include the description of the Khaleefah as a shield, i.e. a protection. So the description of the Imam as a shield is informative of the benefits of the presence of the Imam, thus it is a command for action, because if the information conveyed by Allah (swt) and the Prophet contained rebuke then it is a command of prohibition, and if it contained praise then it is a command for action. If the ordered action is necessary to implement a hukm shar'i (divine law), or by its negligence a hukm shar'i will be neglected, then this command is decisive. In these alhadith there is information also that those who run the affairs of Muslims are Khulafa'a, which indicates an order to appoint them. They also include a prohibition for Muslims to separate from the authority, which indicates the obligation upon Muslims to appoint an authority for themselves, i.e. ruling. Moreover, the Prophet ordered the Muslims to obey the Khaleefah and to fight those who dispute his authority as Khaleefah, which indicates an order to appoint a Khaleefah and to protect his Khilafah by fighting against whosoever disputes with him.
Khilafah is fard - Evidence from the Ijma of the Sahabah
The Ijma' of the Sahabah is a legitimate daleel shar'i (evidence) like the Qur’an and Sunnah of the Messenger of Allah (saw). In regard with the Ijma'a of the Sahabah they all agreed upon the necessity to establish a successor or Khaleefah to the Prophet after his death, and they all agreed to appoint a successor to Abu Bakr, then to 'Umar, then to 'Uthman, after the death of each one of them. Also, all the Sahabah agreed throughout their lives upon the obligation of appointing a Khaleefah. Although they disagreed upon the person to elect as a Khaleefah, they never disagreed upon the appointment of a Khaleefah, neither when the Prophet died, nor when any of the Khulafa'a ar-Rashidun died. Therefore the Ijma'a of the Sahabah is a clear and strong evidence that the appointment of a Khaleefah is obligatory. The extent of the inevitable obligation to establish the Khaleefah and the extent of awareness about this obligation among the Sahabah, is clearly reflected in the actions which they performed at the time. As for the Ijma’ of the companions, they (may Allah be pleased with them) agreed upon the necessity of establishing a successor, (Khaleefah) to the Messenger of Allah (saw) after his death. They all agreed to appoint a successor to Abu Bakr, and upon his death to appoint a successor to ‘Umar and upon ‘Uthman’s death to appoint Ali as a successor to him. The general consensus of Sahabah on the appointment of a Khaleefah manifested itself emphatically upon the death of the Messenger of Allah (saw) and engaged themselves in appointing a successor to him. It is known that the burial of the dead is obligatory, and that it is sinful for those in charge of preparing the burial to engage themselves in anything else until they complete the burial. Despite this, some of the Sahabah engaged themselves in appointing a Khaleefah, even though they were obliged to engage themselves in preparing the burial of the Messenger of Allah (saw). The other Sahabah kept silent about this and participated in the delaying of the burial for two nights, despite having the ability to condemn the delay and being able to bury the Messenger of Allah (saw). This action of the Sahabah is therefore an evidence of consensus to support the fact that the appointment of a Khaleefah is more of an obligation than the burial of the dead and it could not have been legitimate unless the appointment of a Khaleefah were more of an obligation than the burial of the dead.
Furthermore, all the Sahabah consented throughout their lives upon the obligation of appointing a Khaleefah. Although at times they differed about the choice of the Khaleefah, they never disagreed about the fact that a Khaleefah must be appointed, and this was the case in the wake of Allah’s Messenger’s death, and of each of the Khulafa ‘Rashideen’ (The first four Khaleefah). Accordingly, the general consensus of the Sahabah is both a strong and clear evidence that the appointment of a Khaleefah is obligatory.
The appointment of such a Khalifah is obtained through the Bay'aat has been reported on the authority of Nafi that Abdullah ibn Umar said: I heard the Messenger of Allah (may peace be upon him) say: "One who dies without having bound himself by an oath of allegiance (to an Amir) will die the death of one belonging to the days of Jahiliyyah." (Muslim)

Khilafah (Islamic-State) in the view of the Scholars
Khilafah is one of the most important issues in Islam, many versus in Quran and many Hadiths of the Prophet ordered Muslims to establish such a system. Ruling by Islam is the most frequent issue discussed in Quran after the belief and creed. Therefore, Khilafah was discussed by many Muslim scholars, the following are the definition of some of them to Khilafah.
Ibn Khaldoon defined it as: A representation, of the one who has the right to adopt the divine rules, aimed at protecting the Deen and ruling the world (Dunia) with it.
Al-Mawardi defined it as: Succession of the Prophethood aimed at protecting the Deen and ruling the world (Dunia).
Taqiudine al-Nabhani, (founder of Hizb at-Tahreer) defined it as: A total leadership for all the Muslims aimed at implementing the Shariah of Islam and carrying the Message of Islam to the world.
Al-Imam al-Juwaini (known also as Imam Al-Haramain) has a similar definition but I could not translate the text.
In summary, Khilafah is the political system in Islam. It is responsible for implementing the Islamic system (be it social, economic, educational, foreign policy,...) and maintaining its implementation. It is also responsible for spreading the message of Islam to the world. Khilafah is the Islamic state which the Prophet (pbuh) ought to create and worked for in Mecca, for a period of thirteen years, until he (pbuh) established it Medina.
Ibn Hisham, the famous narrator of the Sirah of the Prophet (pbuh) says regarding the establishment of the Islamic State in Madina: "When the Prophet (pbuh) was assured and satisfied in Madina and when his brothers from Muhajireen (migrators) were gathered with him in Madina along with his brothers from the Ansar (helpers), Islam was firmly established so the prayer was established, the Zakah and Sawm (fasting) were obligated, the hudud (punishment) were established, halal and haram was obligated and Islam was in power among them."
The establishment of Khilafah is an Islamic duty. There is a consensus between Muslim scholars about this issue as Al- Qurtubi said in his Tafseer. In one of my previous messages I quoted several scholars from different schools of thoughts in Islam (Sunnah, Shia, Mu'tazilah,...) so I do not need to repeat them here.
The evidence for the duty of establishing the Khilafah is confirmed in the Quran, the Sunnah of the Prophet (pbuh), the consensus of the Sahabah and Shariah principle. I quoted many Ayahs and Hadiths in the previous messages so I will not repeat the evidences from the Quran and Sunnah here, they are available upon request. I will continue with the evidence from the consensus of the Sahabah.
The consensus of the Sahabah means that the Sahabah unanimously accept a certain issue as being a divine rule as they understood it from the Prophet (pbuh). The Sahabah consensus as such is considered a third source of the divine rules (after Quran and Sunnah).
It is reported through Tawatur (via many narration chains) that after the death of the Prophet (pbuh), the Sahabah unanimously prohibited the post of the head of state to be vacant for any time. Abu Bakr (ra) is reported to have said "Muhammad has indeed died. This Deen needs some one to maintain it." Umar Ibn Al-Khatab (ra) said:" There can be no Islam without Jama'a; no Jama'a without an Ameer (leader); and no leadership without obedience."