Some narrations have been related in the Sunni sources concerning the appointment of Abu Bakr by the Holy Prophet (pbuh) as a prayer leader. In case we accept them, some unacceptable complications and ambiguities will arise. Even if it is assumed that the Holy Prophet 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 because there were other people also whom the Prophet (pbuh) had introduced as eligible for leadership in prayers but no one has considered them as qualified for candidacy for succession and caliphate.
The Sunni sources claim that when the Holy Prophet 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 none of which is acceptable.
Muslim (author of Sahih Muslim) quotes "Aisha" as having said: 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 recited the Quran, he (Abu Bakr) would cry, and no one would be able to hear his voice. Aisha asked the Prophet (pbuh) twice or thrice to appoint someone else as a prayer leader but he (the Prophet) said: "Tell Abu Bakr to lead the prayers; truly, you resemble the women in the story of Joseph."
In another tradition, Aisha is quoted as having said that when the Messenger of Allah became ill (the illness that led to the Prophet's demise), Bilal came to ask the Prophet if he would lead the prayer, and he said: "No, tell Abu Bakr to lead the prayer… truly, you resemble the foolish women in the story of Joseph." We sent out for Abu Bakr and he was with the people offering prayers when the Prophet (pbuh) recovered a bit and he walked out of the house with two men supporting him. When Abu Bakr felt the presence of the Prophet (pbuh), he wanted to step back to let the Prophet (pbuh) lead the prayers but the Prophet (pbuh) signaled him to stay on his place. Then the Prophet stood beside Abu Bakr and he followed him (Abu Bakr). So did the people."
As per the story mentioned in Tarikh al-Tabari, the Prophet asked those around him if the time for prayer had set in. 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 man of tender heart. She asked the Prophet (pbuh) to order Umar to lead the prayers. Then the Prophet (pbuh) asked them to tell Umar to lead the congregational prayers. Umar said, "I will not precede Abu Bakr as long as he is present." Then Abu Bakr walked ahead and the Prophet (pbuh) recovered a little from the fever. So he went out of the house and when Abu Bakr heard that the Prophet (pbuh) was coming to the mosque, he moved back and the Prophet (pbuh) pulled his clothe and he himself stood in Abu Bakr's place. The Messenger of Allah sat down (offered the prayers in sitting posture) and he continued the prayers from where Abu Bakr had stopped."
These narrations need to be contemplated over. Many questions arise as to the validity and correctness of these stories, and insofar as those questions are not appropriately answered, one cannot become certain about the authenticity of the narrations. Some of those questions are as under:
Question 1: If the Holy Prophet (pbuh) ordered Abu Bakr to lead the prayers, why did he go to the mosque to lead the prayers despite suffering from a severe illness on account of which he could not walk?
Question 2: Was the Prophet's presence in the mosque an endorsement of Abu Bakr? If so, why did he pull him aside and he himself stood in his place to lead the prayers?
Question 3: If Abu Bakr followed the Prophet (pbuh), as stated in the narration, then it meaningless to say that he led the congregational prayers. The question arises as to whether or not it is possible for a person to be a prayer leader and a follower at the same time and in the same prayer.
Question 4: Which prayer did Abu Bakr lead in the Prophet's stead? Was it Fajr prayer or Zuhr or Isha prayers? Where did Abu Bakr act a prayer leader? Why have the Sunni narrators narrated this story in various and conflicting versions?
Question 5: If this prayer confers any merit upon the leader himself, then why did the migrants, the locals of Medina and also Abu Bakr not put this forward as "proof" on the day of Saqifah?
Question 6: If Abu Bakr's prayer in place of the Prophet (pbuh) confers any merit upon him to become his successor, why was Abdu Rahman bin 'Awf not merited for succession? Haven't the Sunni narrators unanimously quoted the Holy Prophet (pbuh) as saying "Offer prayers behind him" (Abdu Rahman bin 'Awf)?
Question 7: Even if it is assumed that such an incident happened, can it challenge all those explicit traditions from the Holy Prophet (pbuh) about the Commander of the Faithful, Ali (a.s) whose relation to the Prophet (pbuh) was like that of Harun (Aaron) to Moses?
Question 8: If this incident is assumed to be true, why is the Prophet (pbuh) not considered to be delirious on his deathbed when he ordered Abu Bakr to lead the congregational prayers in the mosque but when on the same bed he ordered them to bring pen and paper to write something that would protect them from going astray, then he was described by Umar as being delirious (God forbid!)?
If the Holy Prophet (pbuh) was talking deliriously on his deathbed, then why did you turn to his saying about Abu Bakr’s prayer?! And if he was not talking deliriously, then why did Umar tell others that he was delirious?!
Question 9: When the Holy Prophet (pbuh) was on deathbed, he ordered the companions to join Osama’s army. He said: “Send off quickly the army of Osama. May Allah curse those who retire from Osama's army.
In addition, Osama had not returned until the demise of Holy Prophet, peace and blessings of Allah be upon him and his family. Now the question arises whether Abu Bakr joined Osama’s army or not? If he did not join the army, then he had disobeyed the Prophet’s command. And if he had joined the army, he was not in Medina to lead the prayers in the Holy Prophet’s stead.
Given the above contradictions, how do you say that Abu Bakr offered prayers in place of the Holy Prophet (pbuh)?
Question 10: Why does the Prophet (pbuh) reproach his wives and consider them to be like the foolish women who wanted to misguide Joseph? What had Aisha done to be entitled to the Prophet’s rebuke?!
Considering that these questions remain unanswered, it is difficult to accept that these narrations about Abu Bakr are authentic and reliable. Aren’t these questions sufficient to make us think as to how these injunctions and narrations have been?
 - Sahih Muslim, Kitabl al-Salat, vol.1, pg.313; Sahih Bukhari, Kitab al-Adhan, vol.1, pg.87; Musnad Ahmad bin Hanbal, vol.6, pg.229.
 - Sahih Bukhari, Kitab al-Salat, vol.1, pg.85 and 92; Sahih Muslim, vol.1 vol.1 pg.85 and 92; Musnad Ahmad bin Hanbal, vol.6, pg.210; Sunan Nesai, vol.3, pg.99 and 100.
 - Tarikh al-Tabari, vol.2, pg.230, Beirut Publication.
 - Maghazi, Waqedi, vol.3, pg.1012; Tahzibul Kamal, vol.14, pg.122.
 - Ibid.
 - In order to prevent the Prophet (pbuh) from leaving a Will, Umar said: «دعو الرجل فانه لیهجر!!! حسبنا کتاب الله» “Leave the man (Messenger of Allah) as he is delirious!! The Book of Allah would suffice us.” Apart from the consensus among the Shiite scholars, Sunni scholars have also narrated the same saying in different wordings:
A) Sahih Bukhari, Kitab al-Ilm, Bab Kitabatul Ilm, vol.1, pg.39, vol.2, pg.118 – vol.4, Bab Qawl al-Maridh from “Al-Mardha”, pg.5 – Vol.6, Bab Maradh al-Nabi wa wafatuhu, pg. 11 – Vol.4 Kitab al-Jihad, Bab Jawaez al-Wafd, pg.85.
B) Sahih Muslim, vol.6, Kitab al-Wasiyah, Bab tark al-Wasiyah, pg.76.
C) Sharh Nahjul Balagha ibn Abil Hadid Mu’tazili, vol.2, pg.536 and vol.2 pg.20.
D) Kamil ibn-e Athir, vol.2, pg.217.
 - History of the City of Damascus, Ibn-e Asakir, vol.2, pg.57 and vol.8 pg.60; Mu’jam al-Kabir, Tabarani, vol.3, pg.130; Kanzul Ummal, vol.10, pg.576.
 - Al-Melal wa al-Nehal, Shahristani, vol.1, pg.23; Tarikh Khalifa Ibn Khayyat, pg.63-64; Sharh Nahjul Balagha, Ibn Abil Hadid, vol.6, pg.52.
 - Additionally, if we say that Abu Bakr did not join Osama’s army, he is included in the Holy Prophet (pbuh) because according to some reports as was mentioned in footnote No.8, the Messenger of Allah cursed those who did not go with Osama’s army.
 - Most Sunni historians say that Abu Bakr was in Osama’s army including the following:
Tabaqat al-Kubra, Ibn-e Sa’ad, vol.4, pg.46 and 136; Tahzib ibn-e Asaker, vol.2, pg.391 and vol.3 pg.215; Kanzul Ummal, vol.5, pg.312; Tarikh al-Khamis, vol.2, pg.172; Tarikh Ya’qubi, vol.2, pg.93; Sharh Nahjul Balaghah ibn Abil Hadid, vol.1, pg.53 and vol.2, pg.21.
 - Extracted from Farooq A’zam Ali with minor changes.