The Prophet (ﷺ) went out to affect a reconciliation between the tribes of Bani `Amr bin `Auf and the time of the prayer became due; Bilal went to Abu Bakr and said, "The Prophet (ﷺ) is detained. Will you lead the people in the prayer?" Abu Bakr replied, "Yes, if you wish." So Bilal pronounced the Iqama and Abu Bakr led the prayer. In the meantime the Prophet (ﷺ) came crossing the rows (of the praying people) till he stood in the first row and the people started clapping. Abu Bakr never looked hither and thither during the prayer but when the people clapped too much, he looked back and saw the Prophet (ﷺ) in the (first) row. The Prophet (ﷺ) waved him to remain at his place, but Abu Bakr raised both his hands and sent praises to Allah and then retreated and the Prophet (ﷺ) went forward and led the prayer. (See Hadith No. 295 & 296)
Actions while Praying - Sahih al-Bukhari 1201
This narration from Sahih al-Bukhari demonstrates several important rulings concerning prayer leadership and congregational prayer etiquette. When the Prophet (ﷺ) was delayed in mediating between Bani `Amr bin `Auf, Abu Bakr (may Allah be pleased with him) rightfully assumed leadership of the prayer.
The wisdom in Abu Bakr's conduct is profound - he did not glance around during prayer until excessive clapping indicated an unusual circumstance. This teaches us that unnecessary movements in prayer should be avoided, and looking around is discouraged unless necessary.
The Prophet's gesture for Abu Bakr to remain in place shows the permissibility of gesturing during prayer for valid reasons, while Abu Bakr's humble retreat demonstrates proper respect for the rightful imam. His raising hands in praise to Allah before stepping back illustrates how to properly conclude one's role as prayer leader when the designated imam arrives.
This hadith establishes that if a designated imam arrives after prayer has begun, the current imam should yield leadership, and the prayer remains valid for all participants. The clapping by congregation members, while permissible for women in prayer to alert the imam, is not the preferred method for men, who should rather say "Subhanallah."