Ruling on adding a rak'ah to the prayer out of ignorance by the imam and the follower

Question:
This is a letter sent by the listener Ali Mu'ayyad Musa al-Zahrani, from the land of Zahran. He has two questions in his letter. In his first question, he says:
I prayed Maghrib with my grandfather, and I was one rak'ah behind him. Instead of sitting for the final tashahhud after the third rak'ah, he stood up to perform an extra rak'ah. I held him by the hand and said, "Subhan Allah!" But he insisted on doing so. When he reached this rak'ah, I did not say the taslim; rather, I stood up to complete my prayer with a rak'ah, which was the fourth in number. I did not count his fourth rak'ah as my third. After the prayer ended, I asked him, "Why did you add a rak'ah?" He said, "So that you could complete your prayer with me," out of his ignorance of the ruling. What is the ruling on this addition in his prayer, which was not due to forgetfulness but due to his ignorance of the ruling? What must he do now? And what is the ruling on my prayer, since I added a fourth rak'ah because I did not count his addition, and I also performed the prostration of forgetfulness to compensate for the known addition?

Answer:
As for your action, you were correct when you alerted him and said, "Subhan Allah!" and held him to make him sit; because this is what is obligatory for him: to sit when alerted, and not to perform the addition. And what is obligatory for you is to sit and wait. When he says the taslim, you stand up and perform the rak'ah that you missed, and you do not follow him in the addition. This is what is prescribed.
If the imam stands up for a fourth rak'ah in Maghrib, or for a third in Fajr, or for a fifth in a four-rak'ah prayer, such as Zuhr, then the follower alerts him, saying, "Subhan Allah, Subhan Allah," and the woman claps. It is obligatory for him to return. It is obligatory for the imam to return, unless he is certain that he has not made a mistake and that they are the ones who are mistaken. Otherwise, he must return and sit until he completes his prayer, then say the taslim. He must perform the prostration of forgetfulness before that; before saying the taslim, he performs two prostrations of forgetfulness. If he is certain that they are mistaken and he is correct, he completes his prayer and finishes it.
As for the followers, they act according to their certainty. If they are certain that he is adding, they sit and wait for him until they say the taslim with him. If they are not certain, they follow him and complete the prayer with him; because he is their imam, and it is obligatory for them to follow him, and they have no right to oppose him, unless they are certain that he is mistaken. In that case, they sit and do not follow him in the addition.
And this person who stood up for a fifth rak'ah performed an extra rak'ah out of his ignorance, in order for you to complete the prayer with him. His prayer is valid; because of the ignorance. It is like the one who stands up for a fifth in a four-rak'ah prayer, or a third in a two-rak'ah prayer, or a fourth in a three-rak'ah prayer, out of his ignorance, thinking that he does not return if he stands up and is fully upright. Some people think that if he is fully upright, he does not return, but rather completes it. This is an error due to ignorance. So his prayer is valid due to his ignorance, but he should learn his prayer and understand the jurisprudence of his prayer, so that he does not return to such ignorance.
The point is: if he performs the fifth, or the fourth in a three-rak'ah prayer, or the third in a two-rak'ah prayer, out of ignorance or forgetfulness, his prayer is valid. But he performs the prostration of forgetfulness if it was due to forgetfulness. As for if he intentionally performs the fifth in a four-rak'ah prayer, or the third in a two-rak'ah prayer, or the fourth in a three-rak'ah prayer, such as Maghrib, and he knows the legal ruling, and intentionally stands up, this is playing with the prayer. His prayer is invalid. But generally, this does not happen intentionally; rather, it happens due to ignorance or forgetfulness, so the prayer is valid, and he must perform the prostration of forgetfulness in the case of forgetfulness. The follower must not follow him in the error. If the follower knows that he is mistaken, he does not follow him, but alerts him, and does not follow him, neither in the addition nor in the omission. Rather, the follower acts according to his certainty. If the imam is adding, he sits. If the imam is omitting, the follower stands up to complete what is required of him if the imam does not comply with him. This is what is obligatory for the follower, and this is what is obligatory for the imam, as you heard. Yes.

The presenter: But this person did not count this rak'ah that the imam added for him to complete his prayer as three, and he added a rak'ah from his own side. Is his action correct?

The Shaykh: Yes, he does not follow him in the addition.

The presenter: He followed him and added a rak'ah.

The Shaykh: The follower does not follow in the addition. Yes.

The presenter: He followed him in the addition and added a rak'ah on top of that.

The Shaykh: This is an error, out of his ignorance. The making up of the prayer is after the taslim, after the imam's taslim. So the rak'ah he added before the taslim does not suffice. But because of the ignorance, his prayer is not invalidated, and the completion is after the taslim; because the Shari'ah has established that making up is after the taslim, except in the prayer of fear in some types of the prayer of fear. As for the usual legal making up that the Messenger of Allah (peace and blessings be upon him) explained for the Ummah, it is after the taslim. Yes.

The presenter: So he does not have to repeat the prayer?

The Shaykh: Yes, he does not have to repeat the prayer. Yes.