269 — It is related from Ibn Masʿūd, may Allah be pleased with him, that he said: “The Messenger of Allah ﷺ once led us in prayer. When he concluded with the salām it was said to him, ‘Messenger of Allah, has anything new been revealed concerning the prayer?’ He asked, ‘And what is that?’ They replied, ‘You prayed such-and-such.’ He then folded his legs beneath him, faced the qiblah, and performed two prostrations, after which he made salām again. He then turned to us and said, ‘Had anything new occurred in the prayer I would certainly have informed you of it. But I am only a human being; I forget just as you forget. So if I forget, remind me. And if one of you is uncertain about his prayer, let him strive to determine what is correct, complete the prayer on that basis, and then perform two prostrations.’” Agreed upon.

In another wording recorded by al-Bukhārī: “let him complete (his prayer), then give the salām, and then prostrate.”

Muslim narrates: “The Prophet ﷺ performed the two prostrations of forgetfulness after the salām and after speaking.” ⦗1⦘

Glossary of terms
– “Has anything new occurred in the prayer?” The opening hamzah is interrogative. Ḥadatha (with a fatḥah on the dāl) asks whether some new revelation has come that would alter the established rulings of the prayer by adding to what was previously known.
– “And what is that?” A question asked by someone unaware of what he has done, having neither certainty nor a predominant impression, in contrast to what others have observed.
– “I would have informed you” (anbaʾtukum). Anbaʾa / yunabbiʾu / inbāʾ means “to inform.” Al-nabaʾ means “news,” its plural being anbāʾ.

⦗1⦘ Muslim, Book of Prayer, chapter on forgetfulness prostrations.