Describing the Holy Prophet (SA), the Almighty Allah states in Holy Book Quran:
"Certainly a Messenger has come to you from among yourselves, grievous to him is your falling into distress, excessively solicitous respecting you, to the believers (he is) compassionate, merciful” (Quran, 9:128).
The importance of successor in the life of Holy Prophet (SA)
It can never be believed that the Holy Prophet (SA), who, according to the explicit wording of the Holy Book, Qur'an was the most compassionate and merciful of all, would remain silent all his life and overlook about mentioning one of the divine orders which is undoubtedly of highest importance and topmost priority for the Islamic society and which is demanded by wisdom and commonsense.
The Holy Prophet (SA) knew better than anyone else that the organized and enormous institution of Islam was not a matter of ten or twenty years to be supervised by him. He was aware that Islam is a universal and eternal organization that must direct the human world forever. Thus, the Holy Prophet (SA) predicting the situation of thousands of years after his demise and issued the necessary orders accordingly.
The Holy Prophet (SA) was fully aware that Islam is a social organization and that no social organization can exist and survive even for an hour without a guardian and ruler.
Therefore, the presence of a guardian is necessary to preserve the Islamic sciences and laws of religion, to manage the affairs of the society, and to lead and guide the people towards happiness in this world and the Hereafter. Thus, how could it be conceived that the Holy Prophet (SA) would overlook the situation after his departure and would show no interest towards it?
As a habit, the Holy Prophet (SA) used to appoint someone to manage the affairs of people in his absence whenever he left Madinah even for a few days to take part in battles or to perform Hajj.
Similarly, he also used to appoint governors for cities conquered by the Muslims and used to assign commanders for every division and group that he dispatched to the battlefield. Sometimes, the Holy Prophet (SA) even said: "Your commander is such and such a person. If he is killed, then such and such will be his successor and if he is also killed, so and so will act as the commander."
With this policy that the Prophet (SA) followed, how can it be believed that the Holy Prophet (SA) might not have designated anyone as his successor at the time of his death?
In short, by looking deeply into the sublime aims of Islam and the holy objective of its dignified bearer, one will undoubtedly acknowledge that the matter of Imamah and guardian has been resolved and made clear for the Muslims.
Appointment of a successor by the holy prophet (SA)
The Holy Prophet (SA) did not content himself with only general remarks concerning Imamah and guardianship of the affairs of Muslims after his demise, rather he explicitly explained the subject of Imamah, along with Unity of God and Prophethood, from the very beginning of his call and announced the guardianship and Imamah of 'Ali (AS) for the affairs of the religion and the world as well as for all the affairs of the Muslims.
According to a tradition narrated by Sunni and Shiah on the first day of his call to the people towards Islam, the Holy Prophet (SA) invited his relatives to gather publicly for a meeting.
At this meeting, he explicitly substantiated and established the ministry, guardianship, and succession of the Leader of the Faithful, 'Ali (AS). In the last days of his life, too, in Ghadir Khumm, the Holy Prophet (SA) lifted 'Ali (AS), holding his hand, among the gathering of one hundred and twenty thousand Muslims and stated:
"Anyone for whom I am the guardian and leader, this 'Ali (AS) is his guardian and leader as well."
Furthermore, the Holy Prophet (SA) has specified the number, the names, and all the characteristics of Imams and leaders who will be succeeding him.
In a well-known tradition narrated by Shi'ah and Sunni 'ulama', the Holy Prophet (SA) has stated: "There are twelve Imams, all of whom are from the Quraysh." According to the famous tradition, the Holy Prophet (SA) said to Jabir al-Ansari: "There are twelve Imams." Then he mentioned their names one by one and told Jabir: "You will meet the fifth Imam. Say my salaam (greetings) to him."
Besides, the Holy Prophet (SA) had specifically appointed the Leader of the Faithful, 'Ali (AS), as his successor. Similarly, Imam Ali (AS) had also nominated the next Imam as his successor. In the like manner, each Imam has appointed the next Imam to serve as his successor.
The following sources are used to prepare the above article.
1. Ayatullah Sayyid Muhammad Husayn Tabataba'I, Islamic Techings in Brief, Ansariyan Publication