An imam who was delayed, and another led the congregation in prayer, then ordered them to repeat it

The questioner:
He says: Honorable Shaykh, may Allah grant you success, there is an imam of a mosque who was delayed for his congregation, so one of them stepped forward and prayed with them,

The Shaykh:
Yes.

The questioner:
There is an imam of a mosque who was delayed for his congregation, so one of them stepped forward and prayed with them, and the imam arrived during the prayer, so he waited until they finished the prayer, then he stepped forward and told the ma'mum (those praying behind the imam) that their prayer is invalid, so they must repeat it with him. What is your view on what this imam did, and is his statement correct?

The Shaykh:
If the imam behind whom they prayed was committing a nullifier of the nullifiers of Islam, the prayer behind him is not valid. But if he is a Muslim and upright, then what he did is a mistake and an error, a mistake and an error. It was obligatory for him that they say, "Wait until I arrive, do not rush, do not rush and pray before I arrive." The second time, do not rush. As for him invalidating their prayer, this is a mistake, unless the imam’s prayer is not valid and he knows this about him; that is another matter. But if he innovates, meaning one of the Muslims did the ihsan (excellence in worship) and prayed with the people, you answer him and say, "Your prayer is invalid and the prayer of those behind you is invalid"; this is a great mistake.