The ruling on one who adds a rak'ah in the prayer

Question:
Please, my brother Muhammad from Riyadh, go ahead. Peace be upon you. And upon you be peace. Turn the television down a little, Muhammad. Please repeat that. I have two questions for the Shaykh. The first question: If one adds a rak'ah or two rak'ahs in the prayer, does he repeat it or does he perform the prostration of forgetfulness? Good. And the second question. The second question, may Allah preserve you: If one misses a rak'ah, does he complete it immediately after the imam, or does he wait until the imam finishes the taslim? Good, thank you. Honorable Shaykh, he says: If one adds a rak'ah or more in the prayer, what is the ruling in that?

Answer:
If he added to the prayer intentionally, then his prayer is invalid. If he adds a rak'ah or more, his prayer is thereby invalid. And if he was in a state of forgetfulness and added out of forgetfulness, then he performs the prostration of forgetfulness, and that is sufficient for him, and praise be to Allah. And the question