The ruling on the one who joins the prayer late if the imam adds a rak'ah

The questioner : If the one who joins the prayer late enters with the imam in the second rak'ah and the imam adds a rak'ah, we say that the rak'ah the imam performed, if it is an addition, is a rak'ah that is not prescribed, and it is not counted.

The Shaykh : Yes.

The questioner : So how is it counted for the one who joined late, when it is not prescribed?

The Shaykh : May Allah bless you. The imam is either forgetful or intentional, but he is making up a rak'ah in which he left out al-Fatihah. If it is the second rak'ah, then this number is counted. If it is the first and he was forgetful, then he is excused for it. The ma'mum is also excused, because he is following this imam; he may not know that he entered with him in the second rak'ah, and he may realize it through the tashahhud when he sits, knowing that this is the second.

The questioner : And if he knows, meaning by the shart.

The Shaykh : Meaning in what?

The questioner : Meaning if he entered in the second.

The Shaykh : He knows now that he added, but is this addition invalidating in the prayer? As long as there is a possibility that the imam stood for this fifth because he left out a pillar in one of the rak'ahs, I am not certain that it is an addition.

The questioner : After the prayer, Shaykh.

The Shaykh : What?

The questioner : After the prayer, the imam prays. Yes.

The Shaykh : He said, "I forgot," so the imam's prayer is valid now, and I followed an imam whose prayer is valid.