Q: A person joins a congregational prayer in the third rak‘ah. However, he does not read anything, thinking that the imam is in the first. Does this person have to repeat the prayer?
A: If he realizes this before rukū‘, then it will be obligatory for him to recite Fātiḥah and another chapter. If he happens to realize it in rukū‘ or later, then the prayer is correct and there is no need to do anything. Even though, according to the mustaḥabb caution, he may perform two prostrations of inadvertence for missing out the recitation unintentionally.