Hazrat Abdullah narrates that the Holy Prophet Muhammad (peace and blessings be upon him) once led a prayer, in which he either added to it or shortened it. When he turned to the people after saying salam, the people said, "O Messenger of Allah! Has a new command regarding prayer been revealed?" He asked, "Why, what happened?" The people replied, "You led such and such a prayer today." The Holy Prophet (peace and blessings be upon him) immediately turned his feet and performed two prostrations. Then he said salam and turned towards the people. Then he said, "If any command regarding prayer had been revealed, I would certainly have informed you. In fact, the reality is that I am also a human being like you; just as you forget, I too can forget. When I forget in prayer, remind me." When any of you makes a mistake in prayer, he should reflect and act upon what seems correct to him. Then, when he says salam, he should perform two prostrations.

It is narrated from Hazrat Abu Sa'id that the Messenger of Allah, peace and blessings be upon him, said: When any of you has doubt about his prayer, he should remove the doubt and act upon what is certain. If he is certain that his prayer is complete, he should perform one rak'ah and make two prostrations of forgetfulness (sahw). If his prayer was already complete, then this rak'ah and the two prostrations will become voluntary (nafl). If his prayer was incomplete, then because of this rak'ah it will be completed, and the two prostrations will humiliate Satan.

Hazrat Awn bin Abdullah narrates from his father that I performed four rak'ahs before Zuhr with Hazrat Umar in his room. He said that when you are in doubt about the prayer, perform more (rak'ahs), not less.

Hazrat Ali (may Allah be pleased with him) says that when you have doubt about deficiency or excess in prayer, then perform one more rak‘ah. Because Allah Almighty will not punish for extra prayer. If the prayer was incomplete, it will be completed because of this rak‘ah, and if this rak‘ah turns out to be extra, then there is reward for it.

Hazrat Ali (may Allah be pleased with him) said that if you are in doubt whether you have completed the prayer or not, then complete what you are doubtful about, because Allah the Exalted will not punish for praying more.

Hazrat Abdullah says that if any of you has doubt about the number of units (rak‘ahs) in prayer, then after reflection, act upon what is most likely. If his predominant assumption is that he has prayed three rak‘ahs, then he should pray one more rak‘ah and perform sajdah sahw. If his predominant assumption is that he has prayed four rak‘ahs, then at the end he should only perform sajdah sahw.

Hazrat Abdullah says that he will reflect and perform the prostration of forgetfulness (Sajdah Sahw).

Hazrat Ibn Umar (may Allah be pleased with both of them) used to say that if there is even a thought of deficiency, he should make it complete.

Hazrat Salim says that if someone is in doubt whether he has prayed three rak‘ahs or four, he should free himself from doubt and perform sajdah sahw. Yahya bin Sa‘id says that I mentioned this statement to Hazrat Qasim, so he said, "I also say the same, I also say the same."

4474 - (I mentioned) (1) that to Al-Qasim, and he said: I also say the same (and I also say the same) (2).