Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) led us in the Asr prayer and gave the salam after two rak'ahs. Dhul-Yadayn stood up and said: Has the prayer been shortened, or have you forgotten? The Messenger of Allah (peace and blessings be upon him) said: "Neither of these happened." He said: O Messenger of Allah (peace and blessings be upon him), something did happen. The Messenger of Allah (peace and blessings be upon him) turned to the people and said: "Is Dhul-Yadayn telling the truth?" The people said: Yes, O Messenger of Allah. So the Messenger of Allah (peace and blessings be upon him) completed the rest of the prayer, then, after giving the salam, performed two prostrations while sitting. These are the words of the narration of Qutaybah (may Allah have mercy on him).
Imam al-Shafi'i (may Allah have mercy on him) did not mention his words "Neither of these happened," and said: Then he performed two prostrations while sitting, after the salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3816