Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) led us in prayer. He either added something to it or perhaps omitted something. When the Prophet (peace and blessings be upon him) completed the prayer, we said: O Messenger of Allah (peace and blessings be upon him)! Has a new command regarding the prayer been revealed? The narrator says: The Prophet (peace and blessings be upon him) spread out one of his legs and performed two prostrations of forgetfulness (sajda sahw). Then he said: If a new command regarding the prayer had been revealed, I would have informed you about it, but I am also a human being, I forget just as you forget, so when I forget, remind me. And when anyone is uncertain about his prayer, he should try to determine what is correct, base his prayer on that, and then (at the end) perform two prostrations of forgetfulness.