A Question Concerning the One Who Joins the Prayer Late

Question : The questioner says: A man joined the prayer late, missing one rak'ah. The imam made a mistake and performed an extra rak'ah, and none of the ma'mum (those praying behind him) alerted him. Is this extra rak'ah considered as completing the prayer for the one who joined late?

Answer : This question clarifies that a man who joined late means he missed one rak'ah with the imam, so he entered with this imam, and the imam prayed an extra rak'ah out of forgetfulness, and no one alerted him, so he concluded the prayer. For example, if you entered with the imam in the second rak'ah of the Zuhr prayer, and the imam prayed five rak'ahs for Zuhr, you would have prayed four. So, when the imam concludes the prayer, is it obligatory for you to perform a rak'ah, or do you suffice with the four rak'ahs you caught with him?
Some scholars hold that it is obligatory for you to perform a rak'ah, citing the saying of the Prophet (peace and blessings be upon him) . They say that a rak'ah was missed for you, so you must make it up, because the Prophet (peace and blessings be upon him) says . Others hold that it is not permissible for you to perform a rak'ah after you have prayed four, because if you performed a rak'ah, it would mean that you prayed Zuhr four times and then performed an extra rak'ah intentionally. It is well known that if one performs an extra rak'ah beyond the prescribed number intentionally, his prayer is thereby invalidated. Although the imam is excused due to forgetfulness, you are not excused by it. This is the correct and stronger position: that you do not perform the extra rak'ah.
"If you catch [the prayer], pray with them, and what you missed, complete it." This does not indicate what these scholars held, because the Prophet (peace and blessings be upon him) says, "and what you missed, complete it." It is well known that if I have prayed four, there is nothing left for me to complete. Therefore, the hadith does not serve as evidence that a person makes up this rak'ah, which, if made up, would become an extra in his prayer.