Silsilat al-Ahadith al-Sahihah

Sayyiduna Abdullah bin Buhaina (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) led us in a prayer (and according to one narration, the Zuhr prayer), and after two rak‘ahs, instead of sitting for tashahhud, he stood up. (To alert him) "Subhan Allah" was said, but when the Prophet (peace and blessings be upon him) had stood up straight, he continued the prayer and did not return. The people also stood up following him. The Prophet (peace and blessings be upon him) continued the prayer until he was about to finish it, with only the salam remaining, and the people were also waiting to say the salam. The Prophet (peace and blessings be upon him), due to forgetfulness before the salam, performed two prostrations while sitting and said « اللہ اكبر» for each prostration, then said the salam. The people also performed the prostrations with the Prophet (peace and blessings be upon him).