• I heard Ishaq say: "If a man catches the Imam during an odd number [rak'ah] of his prayer, then when the Imam finishes his prayer, he should stand up and perform what he missed, then prostrate twice. This is reported from Ibn Umar, Abu Sa'id, Ata, Tawus, Mujahid, and Abu Qilabah."

1024 - Ishaq narrated to us, saying: Mu'tamir informed us, saying: I heard my father narrating from Ata, that Ibn Abbas, Ibn Umar, Ibn al-Zubayr, and Abu Sa'id al-Khudri - may Allah be pleased with them - three of these four agreed that if a man misses an odd number [of rak'ahs] of the prayer, he should perform what remains for him, then prostrate twice while sitting.

Chapter: Regarding what requires the two prostrations of forgetfulness

• I heard Ishaq say: "The Sunnah from the Messenger of Allah, peace and blessings of Allah be upon him, has already passed that in every instance of forgetfulness there are two prostrations. So, if you add or subtract from the prayer, or stand up when you should have been sitting, or sit when you should have been standing, or recite aloud when you should have been reciting silently, or recite silently when you should have been reciting aloud, or give the salutation during the first two rak'ahs out of forgetfulness; for all of this, there are two prostrations of forgetfulness."

He said: "Likewise, if you leave out any of the takbirs, or any of the glorifications (tasbih) in bowing and prostration, or any part of what you were commanded to do, it is considered forgetfulness. This is because everything to which the term 'forgetfulness' (sahw) applies to the praying person in any part of his prayer, he should perform the two prostrations of forgetfulness, based on the saying of the Messenger of Allah, peace and blessings of Allah be upon him: 'If one of you forgets in his prayer, let him perform two prostrations.' He did not specify which forgetfulness he meant. This is a known, established, and famous Sunnah, the name of which suffices to understand its nature. So, whenever the term 'forgetfulness' applies to the praying person in his prayer, he should perform the two prostrations of forgetfulness, because if he performs them when they were not due, it is better than leaving them when they were due. Ibrahim al-Nakha'i said the same, and he said: 'In every instance of forgetfulness there are two prostrations.' Al-Hasan ibn Ali once prayed with the people during the day, and they did not see him forget, yet he performed the two prostrations of forgetfulness."