The Most Noble Messenger, peace and blessings be upon him and his family, was well aware that after he had departed for the proximity of his Exalted Lord, the community would lose its unifying foundation, fall into a whirlpool of division and dissent, and be full of struggle and disorder.
The newly established Islamic community was composed of the migrants - including the Bani Hashim, the Bani Umayyah, Adiyy and Taym - on the one hand, and the Helpers (ansar) - subdivided into the Aws and Khazraj tribes - on the other. Once the matchless leader that was the Prophet had departed, ambitions arose on every hand, and instead of being concerned with the interests of Islam, men sought to capture leadership and rule for themselves, wishing to transform divine leadership into tribal rule. The varying aspirations and tendencies that arose heft no firm, unifying bond in place among people, a profound tragedy that the Prophet had foreseen and to which he had alerted his followers: "My ummah will divide into seventy three factions, only one of which will attain salvation, the other factions being destined for hellfire."
The greatest blow that was struck against the unity of Islam after the death of its founder, sowing the seeds of dissension among Muslims, was the difference of opinion relating to the question of rule and leadership. It led to wars, rebellions and bloody struggles, sundering the unity of the Muslims and scattering their unified ranks.
If indeed the Prophet had not made some provision for the painful situation - a situation he foresaw - if he had not attempted to prevent the emergence of the vacuum that would have threatened the very existence of Islamic society, quitting this worldly stage without any plan for safeguarding his ummah from misguidance, would this not have created great problems with respect to government and the administration of affairs? The gravity of future problems was, moreover, apparent even without the receipt of communication from the Origin of Revelation and unseen agents.
How is it possible to imagine that Most Noble Prophet, peace and blessings be upon him and his family, should have neglected nothing in the proclamation of his message but paid no attention to the future course of Islam and its culture, to the guardianship of the truth, and the preservation of both religion and society, entrusting all this simply to the hand of fate and whatever circumstances might later arise? Was it possible that he should not select a captain to steer the ship of the ummah away from the dangerous waves of dissension that he expected it to encounter?
Those who say that the Prophet did not delineate any form of government to succeed him, remaining silent on the subject and leaving his crisis-stricken ummah at a loss what to do - how can they attribute such inappropriate silence and such irresponsible laxity to one whom we know as the Universal Intelligence? It must also be borne in mind that his death did not come suddenly. he realized in advance that he was about to leave the world, In his sermon of the Farewell Pilgrimage (hijjatu 'l-wada') he had proclaimed to the people that he was about to depart from their midst, and that he would not be standing with them at the same place the following year.
Islam was then young, and a long path lay ahead of it if it was to come to fruition. The standard bearer of its movement had committed himself to uprooting all traces of the Jahiliyyah, and to erasing from the hearts and souls of the people any of its residue that might persist He was threatened on two fronts. Internally he was threatened by the Hypocrites who had penetrated the ranks of the Muslims through outwardly ranging themselves beneath the banner of prophethood and were striving repeatedly to defeat the Prophet. In the ninth year of the Hijrah, when he had departed on the Tabuk campaign, he became anxious on account of their intrigues and plotting, and in order to prevent the occurrence of any untoward event he named 'Ali, peace be upon him, as his deputy in Madinah. Externally he was threatened by the two great empires, Byzantium and Persia, and there was the constant fear that at any moment either of those great powers might attack the center of the Islamic movement.
It is evident that confronted with such grave problems the Prophet was bound to place responsibility for the preservation of the ummah in the hands of a person or persons who had the capacity for it, in order that the Islamic call might remain firm and protected.
The first caliph felt a sense of responsibility for the future of the Islamic state and was unwilling for it to be threatened by a vaccum in the leadership. He did not leave the ummah to its own devices, and while on his deathbed instructed the people as follows: "I appoint 'Umar b. al-Khattab as commander and ruler over you; pay heed to his words and obey him." The caliph thus regarded it as his right to designate his own successor and to enjoin obedience to him on the people.
The second caliph likewise realized the need to act quickly once he had been fatally stabbed. He ordered a six-man council to be convened, which implies that he did not grant the Muslims the right of appointing the caliph themselves, otherwise he would not have assigned the task to this council.
The Commander of the Faithful, 'Ali, peace be upon him, accepted the responsibility of the caliphate under extraordinarily complicated and disturbed circumstances, for he was fearful that popular disorder might lead to a wholesale relapse into Jahiliyyah.
Taking all this into consideration, is it at all possible that the Messenger of God, peace and blessings be upon him and his family, should have overlooked the depth of the danger or the sensetiveness of the situation, despite the fact that society had only just emerged from Jahiliyyah, and that he should not have drawn up a plan to confront the dangers he anticipated after his death?
It would indeed be impossible to find any acceptable explanation for a failure on the part of the Prophet to concern himself with this matter. Likewise, it is unimaginable that he should have shown no concern for the future of the summons he had launched, not caring what might become of it after his death.
On the contrary even on his deathbed and while sorely vexed by the pains of sickness, the Prophet was concerned for the ummah and full of anxiety for its future, to the degree that it completely preoccupied his whole being.
During those sensitive and critical moments, when everyone was in a state of shock and bewilderment and some of the Companions (sahabah) including 'Umar b. al-Khattab were gathered around his bed, the Prophet said: "Bring me paper and an inkpot; I wish to write instructions for you so that you never go astray."
This effort of the Prophet, peace and blessings be upon him and his family, preserved in a tradition on the authenticity of which are agreed, is clear testimony to the fact that the Messenger of God, precisely at the time that he was spending the last moments of his luminous life, was concerned for the future of Islam and was giving thought to the dangers that would arise after his death. He wished to lay down a path for the future in order to preserve the ummah from deviation and society from degeneration, for he understood these matters better and more profoundly than anyone.
A matter that. deserves particular attention is the question of successorship in heavenly religions and laws, for all the prophets of God selected deputies and successors in accordance with revelation. For example, Adam, Ibrahim (Abraham), Ya'qub (Jacob), Musa (Moses) and 'Isa (Jesus), peace be on them all, selected their successors, all of whom are known to us by name. 
The Most Noble Messenger, peace and blessings be upon him and his family, said: "Every prophet has a legatee (wasiyy) and an heir (warith), and 'Ali is my legatee and heir."
Since according to the Qur'an the norms of God are fixed and unchanging, it follows that the Prophet of Islam must also act in accordance with this immutable divine norm by presenting his own deputy and successor to the Islamic ummah. This indeed is what happened. In conformity with God's command and as required by prophethood and the need to perpetuate the message of Islam and implement its goals, he selected his legatee, thus making its duty clear to the ummah. All of this represents a belief that originates in the Book of God.
Muslims are unanimous in believing that the Prophet of Islam, peace and blessings be upon him and his family, never made any mention of Abu Bakr or the two caliphs that followed Abu Bakr as his caliphs and successors, nor is there any indication of their caliphate in the Qur'an and the Sunnah. The caliphate of Abu Bakr is thus a simple historical event, not an indisputable religious belief, so that every Muslim has the right to express an opinion on the matter in accordance with his own understanding, as simple logic requires.
 Ibn Majah, al-Sunan, "Bab al-Fitan."
 al-Ya'qubi, al-Tarikh, Vol. II,
 Ahmad b. Hanbal, al-Musnad, Vol.
I, p. 344; Ibn Sa'd, al-Tabaqat, Vol. II, p.242; al-Bukhari, al-Sahih;
Vol. I, p. 22; al-Tabari, Tarikh, Vol. II, p.436.
 al-Mas'udi, Ithbat al-Wasiyyah;
 Ibn , Asakir, al-Tarikh, Vol. III, p. 5; Riyad al-Nadirah, Vol. II, p. 178.