The Sunni historians claim that when Muhammad Mustafa was unable to attend the public prayers because of his illness, he ordered Abu Bakr to lead the congregational prayers, and they put this forward as “proof” that he wanted him (Abu Bakr) to become his successor.
There are various versions of this story extant. According to one, Bilal came to ask the Prophet if he would lead the prayer, and he said: “No, tell Abu Bakr to lead the prayer.”
There is a second version in which at prayer time, the Prophet asked a certain Abdullah bin Zama'a where was Abu Bakr. Ibn Zama'a went out to call Abu Bakr but could not find him. But he found Umar, and asked him to lead the prayer. But when Umar called the takbir (Allah-o-Akbar), the Prophet heard him, and said: “No! No! Allah and the believers forbid that. Tell Abu Bakr to do so.”
As per the third story, the Prophet asked those around him if the time for prayer had come. They said that it had, whereupon he asked them to tell Abu Bakr to lead the congregation. But his wife, Ayesha, said that her father was a very tenderhearted man, and if he saw his (the Prophet's) place in the mosque empty, he (Abu Bakr) would cry, and no one would be able to hear his voice. But he (the Prophet) insisted that Abu Bakr act as the prayer-leader.
There are some other stories also like these in the history books and the substance of them all is that Abu Bakr led the congregation in prayer(s) during the last days of the Prophet on this earth.
Muhammad ibn Ishaq
Ibn Shihab said, Abdullah b. Abu Bakr b. Abdur Rahman b. al-Harith b. Hisham told me from his father from Abdullah b. Zama'a b. al-Aswad b. al-Muttalib b. Asad that when the Apostle was seriously ill and I with a number of Muslims was with him, Bilal called him to prayer, and he told us to order someone to preside at prayer. So I went out and there was Umar with the people, but Abu Bakr was not there. I told Umar to get up and lead the prayers, so he did so, and when he shouted Allah Akbar, the Apostle heard his voice, for he had a powerful voice, and he asked where Abu Bakr was, saying twice over, “God and the Muslims forbid that.”
So I was sent to Abu Bakr and he came after Umar had finished that prayer and presided. Umar asked me what on earth I had done, saying, “When you told me to lead the prayer, I thought that the Apostle had given you orders to that effect; but for that I would not have done so.” I replied that he had not ordered me to do so, but when I could not find Abu Bakr I thought that he (Umar) was most worthy of those present to lead the prayer. (The Life of the Messenger of God)
Foregoing is the earliest extant account of the story that Abu Bakr led the prayers. Its narrator was Abdullah b. Zama'a. He himself says that the Apostle ordered him to ask someone which means anyone, to lead the prayer, and he did not specifically mention Abu Bakr. Even later, when the Apostle forbade Umar to lead the prayer, he did not order Abu Bakr to take his place. He merely asked where was Abu Bakr.
Abdullah b. Zama'a thought that Umar was “most worthy” to lead the prayer but the Apostle of God did not agree with him.
Sir William Muir
It is related that on one occasion Abu Bakr happened not to be present when the summons to prayer was sounded by Bilal, and that Umar having received, as he erroneously believed, the command of Mohammed to officiate in his room, stood up in the mosque, and in his powerful voice commenced the Takbir, “Great is the Lord!” preparatory to the service. Mohammed overhearing this from his apartment, called out with energy, “No! No! No! The Lord and the whole body of believers forbid it! None but Abu Bakr! Let no one lead the prayer but only he.” (The Life of Mohammed, London, 1877)
As stated above, according to the Sunni historians, the purpose of the Apostle in ordering Abu Bakr to lead the prayers was to “promote” the latter as his successor.
It is entirely possible that Abu Bakr led the Muslims in prayer in the lifetime of the Apostle himself. What, however, is not clear is if he did so at the orders of the Apostle, or, at least with his tacit approval. The claim that Abu Bakr led the prayers at the orders of the Prophet is open to question because he was a subaltern in Usama's army, and the Apostle had ordered him to leave Medina and to report to his Commanding Officer at Jorf which, apparently, he never did.
Even if it is assumed that the Apostle ordered Abu Bakr to act as an Imam (prayer-leader), it is still not clear how it became an “endorsement” of his candidacy for succession. After all, Abu Bakr himself, Umar bin al-Khattab, and Abu Obaida ibn al-Jarrah, all three had served under Amr bin Aas in the campaign of Dhat es-Salasil, and had offered their prayers behind him for many weeks. Amr bin Aas had made it plain to all three of them that he was their boss not only in the army but also as a leader in religious services.
As already noted, the Sunni Muslims assert that the Prophet chose Abu Bakr to lead the public prayers just before his death because he wanted the latter to be his khalifa.
Ibn Hajar Makki, a Sunni historian, says in his book, Tatheer al-Janan (page 40):
“Abu Bakr led Muslims in prayer (at the orders of the Apostle). It is, therefore, the consensus of all scholars that his khilafat was by the fiat of the Apostle.”
But the same Sunnis also hold the view that leading other Muslims in prayer does not confer any merit upon the leader himself, and that it is not necessary for a man to be “qualified” to act as an Imam (prayer-leader). In this connection, they quote the following “tradition” of the Prophet of Islam on the authority of Abu Hurayra:
Abu Hurayra reports that the Apostle of God said that:
“Prayer is a mandatory duty for you, and you can offer it behind any Muslim even if he is a fasiq (even if he commits major sins).”
According to this “tradition” a fasiq (sinner) is just as well qualified to be an Imam (prayer-leader) as a saint; in the matter of acting as Imam, the sinner and the saint enjoy parity!
John Alden Williams
And hearing and obeying the Imams and the Commanders of the believers (is necessary) - whoever received the Caliphate, whether he is pious or profligate, whether the people agreed on him and were pleased with him or whether he attacked them with the sword until he became Caliph and was called “Commander of the Believers.”
Going on a holy war (Jihad) is efficacious with a pious or with a dissolute commander until the day of Resurrection; one does not abandon him. Division of the spoils of war and applying the punishments prescribed by the Law is for the Imams. It is not for anyone to criticize them or contend with them. Handing over the alms-money to them (for distribution) is permissible and efficacious; whoever pays them has fulfilled his obligation whether (the Imam) was pious or dissolute.
The collective prayer behind the Imam and those he delegates is valid and complete; both prostrations. Whoever repeats them is an innovator, abandoning the tradition and opposed to the Sunna. There is no virtue in his Friday prayer at all, if he does not believe in praying with the Imams, whoever they are, good or bad; the Sunna is to pray two prostrations with them and consider the matter finished. On that let there be no doubt in your bosom. (Some Essential Hanbali Doctrines from a Credal Statement in Themes of Islamic Civilization, p. 31, 1971).
According to the Hanbali verdict quoted above, anyone and everyone can lead the Muslims in prayer. Abu Hurayra and Abu Sufyan are as much qualified to become prayer-leaders as Abu Bakr.
This opinion was formulated by the later generations of the Muslims. One man who didn't share it with them, was Muhammad Mustafa, the Interpreter of God's Last Message to mankind. He considered Umar bin al-Khattab “unqualified” to lead the Muslims in prayer, and forbade him to do so.
The Shia Muslims discount as spurious the “tradition” which Abu Hurayra has attributed to the Prophet of Islam that it is lawful to offer prayer behind anyone, even a fasiq. They say that an Imam (a prayer-leader) must be:
A man of good reputation, i.e., one known to possess good character.
The story that Abu Bakr led Muslims in prayer in the lifetime of the Prophet, is either true or it is false. If it is true, then it means that he carried out a duty which according to Abu Hurayra and the Sunni jurists and scholars, anyone and everyone else was qualified to perform, and it did not make him “special” in any way; if it is false, then it means that he did not lead any prayer-meeting at all when the Prophet was still alive.
But if this report is true, then it also means that any prayer offered behind Umar bin al-Khattab, is void. The Prophet said that God Himself didn't want Umar to act as prayer-leader. Umar's insistence upon leading the Muslims in prayer, before or after the death of the Prophet, could not possibly make those prayers less unacceptable to God!