What is the ruling on the prostration of forgetfulness (sujood as-sahw) in cases of doubt regarding an increase or decrease in the prayer, whether the worshipper becomes certain before the salutation (tasleem) or after it?

Imam Al-Nawawi affirms that scholars have unanimously agreed that the Hadith which states: "If a ruler strives and is correct, he has two rewards; and if he strives and errs, he has one reward," applies to a ruler who is qualified to rule. As for someone who is not qualified, it is impermissible for him to rule, and if he does rule, his correctness is coincidental, he is sinful, and his ruling is void.

Regarding doubt in prayer, if an Imam or a person praying alone doubts the number of rak'ahs, they should base their decision on certainty, which is the lesser number, then complete their prayer and perform the prostration of forgetfulness (sujud al-sahw) before the tasleem. In this case, one does not rely on the predominant opinion, and this is the view of the majority. However, if one doubts an increase or decrease after the tasleem, they do not perform the prostration of forgetfulness unless they are certain of it.

As for congregational prayer, if the congregants alert the Imam to his omission of the first tashahhud, he performs the prostration of forgetfulness before the tasleem. If they alert him shortly after the tasleem, he prostrates and does not return to the tashahhud. If a long time has passed, he does not prostrate. If the Imam omits a pillar or a rak'ah, he is not permitted to make the tasleem before performing it. If he does so knowingly and intentionally, his prayer is void and he must repeat it, as the prostration of forgetfulness does not suffice for a pillar or a rak'ah.