What did the Prophet Muhammad (peace be upon him) do when the people in the mosque noticed he had offered two rak'ahs instead of four?
 Ibn Sirin reported Abu Huraira as saying:                      The Messenger of Allah (may peace be upon him) led us in one of the two evening prayers, Zuhr or 'Asr, and gave salutations after two rak'ahs and going towards a piece of wood which was placed to the direction of the Qibla in the mosque, leaned on it looking as if he were angry. Abu Bakr and Umar were among the people and they were too afraid to speak to him and the people came out in haste (saying): The prayer has been shortened. But among them was a man called Dhu'I-Yadain who said: Messenger of Allah, has the prayer been shortened or have you forgotten? The Apostle of Allah (may peace be upon him) looked to the right and left and said: What was Dhu'I-Yadain saying? They said: He is right. You (the Holy Prophet) offered but two rak'ahs. lie offered two (more) rak'ahs and gave salutation, then said takbir and prostrated and lifted (his head) and then said takbir and prostrated, then said takbir and lifted (his head). He (the narrator) says: It has been reported to me by Imran b. Husain that he said: He (their) gave salutation.