What is the ruling on someone who sat after the first rak'ah in a four-rak'ah prayer, then remembered before the tasbeeh and stood up to perform the prostration of forgetfulness (sujood al-sahw) before the salutation? Is his action considered an act of forgetfulness? And what is the ruling on a congregant (ma'mum) who did not forget but performed the prostration of forgetfulness with the imam? And what is the ruling on one who did not forget and did not perform the prostration of forgetfulness with the imam?

Scholars have differed regarding whether the Imam, after the second prostration in the first rak'ah, should perform the prostration of forgetfulness (sujood as-sahw) if he sits inadvertently:

Some say he performs the prostration of forgetfulness if his sitting was prolonged. This is the view of the Shafi'is and Malikis.

Others say he performs it unconditionally, even if the sitting was not prolonged, due to the generality of the Prophet's (peace be upon him) saying: "If a man adds or subtracts, he should prostrate twice." This is the view of thebalis.

The prostration of forgetfulness is performed before the salutation (taslim) according to the Shafi'is and Hanbalis.

The congregants (ma'moomoon) are obliged to follow him in the prostration of forgetfulness, whether they caught one rak'ah with him or less or more, because of the Prophet's (peace be upon him) saying: "Indeed, the Imam is appointed to be followed." Whoever intentionally fails to follow him, their prayer becomes invalid.

Some have gone to the extent of saying that if a congregant caught less than one rak'ah, he does not perform the prostration of forgetfulness with the Imam, but the first opinion is closer to the evidence.