In a previous fatwa (F 248), we discussed the ruling on mistakes in the recitation of the Qur᾽ān during prayer and the differing opinions among the schools of Islamic thought regarding its validity.
In the case mentioned in the question, the reciter did not make the mistake intentionally and was not aware of it at the time. It happened due to an involuntary cause, and the alteration did not change the meaning to something contrary or invalid. Therefore, his prayer and the prayer of those behind him are valid according to the late Ḥanafī scholars and the sound opinion of the Mālikī school. There is no need for him or the congregation to repeat the prayer.
Fatwā issued by Dr. Khālid Naṣr