One of them after the other without the first having invalidated his ablution, if the first leaves the leadership after having already entered into it, then the second steps forward and completes the prayer from the place where the first had reached, and the permissibility of the prayer of the one who is led, being an imam in part of the prayer and a follower in part of it, and the permissibility of a person following an imam when the follower began the prayer before his imam.

It is narrated from Sayyiduna Sahl bin Sa’d (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) went to the people of Banu Amr bin Awf to reconcile between them. (He, peace be upon him, was delayed there) and the time for prayer arrived. The muezzin came to Sayyiduna Abu Bakr (may Allah be pleased with him) and said,“Will you lead the people in prayer so that I may pronounce the iqamah?”He replied,“Yes.”Thus, Sayyiduna Abu Bakr (may Allah be pleased with him) began to lead the people in prayer. Meanwhile, as the people were praying, the Messenger of Allah (peace and blessings of Allah be upon him) also arrived. He made his way through the rows until he stood in the first row. At this, the people clapped (to draw the attention of Sayyiduna Abu Bakr, may Allah be pleased with him), but Sayyiduna Abu Bakr (may Allah be pleased with him) would not turn his attention here and there in his prayer. Then, when the people clapped even more, he became attentive and saw the Messenger of Allah (peace and blessings of Allah be upon him). The Messenger of Allah (peace and blessings of Allah be upon him) signaled to him to remain standing in his place (and continue the prayer), but Sayyiduna Abu Bakr (may Allah be pleased with him), upon this command of the Messenger of Allah (peace and blessings of Allah be upon him) (that he should lead the people in prayer in his presence), raised both his hands and thanked and praised Allah Almighty. Then Sayyiduna Abu Bakr (may Allah be pleased with him) stepped back and stood in line with the rows, and the Messenger of Allah (peace and blessings of Allah be upon him) moved forward and led the prayer. Then, when the prayer was finished, he said:“When I had commanded you, why did you not remain standing in your place?”So Sayyiduna Abu Bakr (may Allah be pleased with him) replied,“It does not befit the son of Abu Quhafah (Abu Bakr) to lead the prayer in front of the Messenger of Allah (peace and blessings of Allah be upon him).”Therefore, the Messenger of Allah (peace and blessings of Allah be upon him) said:“What is the reason that I saw you clapping so much? Whoever experiences something in the prayer (i.e., the imam makes a mistake), he should say «‏‏‏‏سُبْحَانَ اللَٰه» ‏‏‏‏. For when he says «‏‏‏‏سُبْحَانَ اللَٰه» ‏‏‏‏, the imam will turn his attention towards him, and indeed, clapping (to alert the imam to a mistake) is specific for women.”This hadith is narrated by Yunus bin Abdul A’la. Imam Abu Bakr (may Allah have mercy on him) says that in this hadith is evidence for the issue that when the imam is alerted by saying «‏‏‏‏سُبْحَانَ اللَٰه» ‏‏‏‏, it is permissible for the imam to turn his attention towards the one who says «‏‏‏‏سُبْحَانَ اللَٰه» ‏‏‏‏, so that he may know what mistake the one who said «‏‏‏‏سُبْحَانَ اللَٰه» ‏‏‏‏ has found, and thus fulfill his duty accordingly.