If a person considers a word that he has learned to be correct and recites it in the same way in prayers, and he later realises that it was wrong, it is not necessary for him to repeat his prayers.
Ruling 988.* If a mukallaf does not know the fatḥah and kasrah of a particular word, or, for example, he does not know whether a particular word is spelt with a ‘ه’ or a ‘ح’, then he must perform his duty in some way; for example, he must learn it, or perform prayers in congregation, or recite it in two or more ways so that he is certain that he has recited it correctly.
However, in such a case, his prayer is deemed to be valid only if that wrong sentence can be commonly considered part of the Qur’an or a dhikr.