Question: A man missed some rakaat [of the congregational prayer] and during his standing to complete what he missed after the tasleem of the Imam, a group entered the masjid. They pushed him forward as the Imam. Is this action correct?
Answer: “Yes, this action is correct. This man moves from being the one lead to the one leading. When he completes his prayer, those who joined stand to complete their prayer if they joined after the first Takbir”.
[Taken from: https://audio.islamweb.net/audio/index.php?page=FullContent&audioid=316045#333226]
Faisal Ibn Abdul Qaadir Ibn Hassan