Sahih al-Bukhari 6051

Abu Hurayra reported that the Prophet led us in the noon prayer and prayed two rakahs, then said the salutation and stood by a piece of wood at the front of the mosque, placing his hand on it. Abu Bakr and Umar were among the people, but they were too awed to speak to him. The people who left quickly said, “The prayer has been shortened.” Among the people was a man whom the Prophet called Dhu al-Yadayn. He asked, “Prophet of Allah, did you forget, or has the prayer been shortened?” He replied, “I did not forget, and it has not been shortened.” They said, “Rather, you forgot, Messenger of Allah.” He said, “Dhu al-Yadayn has spoken the truth.” He stood, completed two rakahs, said the salutation, then said Allahu akbar and prostrated as long as, or longer than, his usual prostration. He raised his head saying Allahu akbar, prostrated again for as long as, or longer than, his usual prostration, then raised his head saying Allahu akbar.