(a) It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) led the prayer and either left something out of it or added to it. Ibrahim (may Allah have mercy on him) said: This uncertainty (about whether it was less or more) is from me. It was said to him (peace and blessings be upon him): O Messenger of Allah! Has something been added to the prayer? He (peace and blessings be upon him) said: "I am only a human being; I forget just as you forget. So when any of you forgets in the prayer, he should perform two prostrations while sitting." Then the Messenger of Allah (peace and blessings be upon him) turned back and performed two prostrations.
(b) In this hadith and in the narration of al-Aswad (may Allah have mercy on him) from Abdullah (may Allah be pleased with him), his (peace and blessings be upon him) prostrations came after his saying: "I am only a human being."
(c) The narration of Mansur (may Allah have mercy on him) from Ibrahim (may Allah have mercy on him) has already passed, which indicates that he (peace and blessings be upon him) first prostrated, then gave the salam, and then, after giving the salam, turned to the people and said what he said.
(d) In this chapter, a narration like that has already passed from Ibrahim bin Suwayd (may Allah have mercy on him) through Alqamah (may Allah have mercy on him), and it is more worthy of being correct than the narration of one who did not keep to the order of events in relating it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3843