Ruling on performing congregational prayer when a man is praying alone in the mosque

The first message in this episode came from the questioner Abdullah ibn Nasser ibn Saif from ad-Dalim. He says: If several people enter the mosque and find a man praying alone, and he has already completed part of his prayer, should they follow him as their imam, or should one of them step forward to lead them? Please inform us; may Allah reward you.
Answer: In the name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, and may Allah send blessings and peace upon the Messenger of Allah, upon his family and his Companions, and upon those who follow his guidance.
To proceed: It is prescribed for these people who enter to pray in congregation; indeed, this is obligatory upon them. If they see that the one who preceded them is qualified to be an imam, and they appoint him and pray behind him, that is better so that the congregation is larger. If they see that he is not qualified for that, they should pray on their own and choose as their imam the one among them who is most suitable for leading prayer over that first person who preceded them; that is better and more appropriate. Yes.
The presenter: May Allah reward you.