What is the ruling if the imam forgets and stands in the third rak'ah without sitting for the first tashahhud, and is it obligatory for the believers to say to him, "Subhan Allah"?

The questioner : Noble Shaykh, what is the ruling if the imam forgets and stands in the third rak'ah without sitting for the first tashahhud, and is it obligatory for the ma'mum to say to him, "Subhan Allah," or not? I hope for your guidance.

The Shaykh : Praise be to Allah, Lord of the worlds, and I send prayers and peace upon our Prophet Muhammad, the Seal of the Prophets and the Imam of the Pious, and upon his family and his Companions, and those who follow them with excellence until the Day of Judgment:
Forgetfulness in prayer is a matter for which a person is not blamed, because every human being forgets. For this reason, it occurred to the most perfect of people in humility, the Messenger of Allah (peace and blessings be upon him). He forgot in his prayer, so he prayed five rak'ahs once, and he prayed two rak'ahs and said the taslim from the Zuhr or 'Asr prayer once. He also left the first tashahhud once, so he stood up without sitting, and he (peace and blessings be upon him) said: .
The ruling on sujud al-sahw is obscure to many people. I do not say only to the general public, but to both the general public and the specialists; some of its rulings may be difficult for them. What is obligatory for imams, in particular, is to know the rulings of this chapter so that if they encounter it, they worship Allah in it with knowledge. Therefore, I would like to mention a summary of its rulings while answering the questioner's question. I say:
There are three causes for sujud al-sahw: addition, omission, and doubt.
As for addition: this is like a person adding a ruku' in a place where it does not belong, or a sujud in a place where it does not belong, or sitting in a place where it does not belong, or standing in a place where it does not belong. For example, bowing twice in one rak'ah, or prostrating three times, or standing in a place where one should sit, or sitting in a place where one should stand. If a person intends this addition, meaning he intends to bow twice, or prostrate three times, or stand in a place where he should sit, or sit in a place where he should stand, if he intends that, his prayer is invalid. This is based on the saying of the Prophet (peace and blessings be upon him): . It is known that two ruku's in one rak'ah, other than in the eclipse prayer, or three prostrations in one rak'ah, are not in accordance with the command of Allah and His Messenger, so it is invalid and rejected.
As for if it happens to him by forgetfulness, his prayer is not invalid, but he must sit for the sujud al-sahw, and his prostration is after the taslim. The evidence for this is that when the Prophet (peace and blessings be upon him) forgot in his prayer and prayed five rak'ahs, he prostrated two prostrations after he said the taslim, when they reminded him of it after his taslim. The aspect of the indication from this hadith is that when the Prophet (peace and blessings be upon him) prostrated the two prostrations after they reminded him of the addition, he did not say, "If one of you adds, let him prostrate before he says the taslim." Rather, he left the matter as it was.
Another piece of evidence is that the Prophet (peace and blessings be upon him) said the taslim from two rak'ahs in a four-rak'ah prayer, Zuhr or 'Asr. They reminded him, so he completed his prayer and said the taslim, then he prostrated two prostrations after he said the taslim. This is sujud for an addition, because the imam added the taslim during the prayer. So we derive from this a rule: that sujud al-sahw, if its cause is addition, is after the taslim. Just as this is the requirement of the evidence from the athar, meaning the requirement of what came in the Sunnah, it is also the requirement of the theoretical evidence, which is that the prostration is after the completion of the prayer so that two additions do not gather in the prayer. This is the ruling on prostration for addition.
As for prostration for omission: this does not occur except in the omission of obligatory acts. It is before the taslim. An example of this is if a person forgets to say, "Subhan Rabi al-A'la," while he is prostrating, then he prostrates for sujud al-sahw before the taslim, and his prayer is valid. Similarly, if he forgets the first tashahhud, as in the questioner's question, until he stands and relies on his standing, he does not return to it, but he continues in his prayer and prostrates for sujud al-sahw before the taslim.
As for doubt: this is the third cause. Doubt is either after the completion of the prayer, or it is an illusion with no reality, or it is from a person who is prone to frequent doubts such that he does not pray without doubt occurring in him. In these three cases, it is not considered anything, meaning this doubt is not considered anything. So if the praying person, when he says the taslim, doubts whether he prayed a complete prayer or an incomplete one, this doubt does not harm him because he has finished his worship. The original state is that he performed it in the required manner, so this doubt has no effect. Also, if we opened this door, Satan would have power over every person who performs worship to make him doubt it after he finishes it. So we close the door on Satan and say: doubt after the completion of worship has no effect. Yes, if he is certain, then he acts according to his certainty.
Let us give an example of this: if a person who performed wudu' finished and then doubted whether he wiped his head or not. We tell him: this doubt has no effect, proceed to what you want, and your wudu' is complete, unless he is certain that he did not wipe his head. In that case, he acts according to his certainty, wipes his head, and washes his feet if he remembers it in a short time.
Similarly in prayer, if a person says the taslim from the Zuhr prayer and doubts whether he prayed three or four, we say: this doubt has no effect, do not pay attention to it, do not prostrate for sujud al-sahw, and do not perform a rak'ah. The work is finished, unless you are certain that you did not pray except three. In that case, you perform the fourth, prostrate for sujud al-sahw, and say the taslim if you remember it in a short time. And if you remember it after a long time has passed, it is obligatory for you to repeat the prayer from the beginning.
The second type of doubt that is not considered is if a person is prone to frequent doubts. In this case, the doubt is not considered and is not paid attention to, because a person prone to frequent doubts is outside the original nature of humans, so this doubt is a disease and waswas (whispers) that is not paid attention to. Accordingly, if a person doubts every time he prays whether he completed it or not, we say: do not pay attention to this doubt, rather ignore it as if it were nothing. The third: if the doubt is an illusion, meaning a mere illusion and not a real hesitation, then it is also not paid attention to and does not affect him, because it is a type of waswas.
What remains for us is if the doubt is real during the prayer, such as doubting whether he prayed three or four. We say that this doubt does not escape two states:
The first state: that he has a preference between the two sides. He acts according to the stronger position, completes his prayer, and prostrates for sujud al-sahw after the taslim.
The second state: that there is no preference, but the doubt is equal on both sides. He builds on the lesser here because he is certain, completes his prayer, and prostrates for sujud al-sahw before the taslim.
With this, we have known that doubt sometimes requires prostration before the taslim and sometimes after the taslim. If the doubt has a preference for one of the two possibilities, he acts according to the stronger position, completes his prayer, and prostrates after the taslim. And if the doubt has no preference for one of the two possibilities, but they are equal, he acts according to the lesser, completes his prayer, and prostrates for sujud al-sahw before the taslim. With this detail, the Sunnah came. Accordingly, we give two examples:
The first example: a man is praying Zuhr and doubts whether this is the third or the fourth rak'ah, and it is more likely to him that it is the fourth. We say: this is the last of your rak'ahs, so say the taslim, then prostrate for sujud al-sahw after the taslim. If it is more likely to him that this rak'ah is the third, we say: this is the third, so perform a rak'ah, say the taslim, and prostrate for sujud al-sahw after the taslim.
The second example: a man is praying Zuhr and doubts in the rak'ah whether it is the fourth or the third, and nothing is more likely to him. In this case, we say: make it the third, because it is the lesser, and complete the prayer, meaning perform the fourth, and prostrate for sujud al-sahw before the taslim, because the doubt here has no preference. The doubt that has no preference is one in which a person builds on certainty, which is the lesser, and prostrates for sujud al-sahw before the taslim.
Here is an issue: if a person builds on certainty or on the more likely, and then it becomes clear to him that he was correct in what he did, does he prostrate for sujud al-sahw or not?
There are two opinions among the scholars: some said: he does not prostrate, because the doubt was removed by certainty, and it became clear that his action had no addition or omission.
And some said: he prostrates, because he performed a part of his prayer while hesitating in it, so to compensate for this hesitation, he prostrates for sujud al-sahw.
An example of this: a man is praying Zuhr and doubts whether he is in the third or the fourth, hesitating in it with no preference. What do we tell him?
We say: build on certainty, which is the lesser, so make this the third and perform a rak'ah. So he did, and when he was in the final tashahhud, he remembered that this was certainly the fourth. Does he prostrate for sujud al-sahw or not?
There is the scholarly disagreement I mentioned. If he prostrates, that is better, and if he leaves it out, there is no blame on him.

The questioner : May Allah bless you.