Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) led us in one of the prayers after the sun's decline, either Zuhr or Asr, but my strongest belief is that it was Asr. He (peace and blessings be upon him) led two rak'ahs, then after giving the salam he stood leaning against a piece of wood in the mosque, and he (peace and blessings be upon him) was very angry. The people who hurry out left, saying: The prayer has been shortened, the prayer has been shortened. Among the people there were Sayyiduna Abu Bakr and Sayyiduna Umar (may Allah be pleased with them both), and they too were too awed to speak. A man named Sayyiduna Dhu al-Yadayn (may Allah be pleased with him) stood up and said: O Messenger of Allah, have you forgotten, or has the prayer been shortened? He (peace and blessings be upon him) asked: "What is Dhu al-Yadayn saying?" The Companions (may Allah be pleased with them) said: O Messenger of Allah, he is speaking the truth. So the Messenger of Allah (peace and blessings be upon him) led us in two rak'ahs, then gave the salam, then said the takbir and prostrated, then raised his head from the prostration saying the takbir, then said the takbir and prostrated like his usual prostrations or longer, then raised his head saying the takbir.
(b) Muhammad states: I was informed via Sayyiduna Imran bin Husayn (may Allah be pleased with him) that he said: "And he gave the salam."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3894
(a) Imran bin Husayn (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) gave the salam after leading three rak'ahs of the Asr prayer, and stood up and went into the room. Dhu al-Yadayn (may Allah be pleased with him) stood up and said: O Messenger of Allah, has the prayer been shortened? So he (peace and blessings be upon him) came out in a state of anger and led the rak'ah that had been left, then performed the two prostrations of forgetfulness and gave the salam.
(b) Imam Muslim (may Allah have mercy on him) recorded this hadith in his Sahih from Ishaq bin Ibrahim (may Allah have mercy on him), but in it he said: He (peace and blessings be upon him) led the rak'ah that had been left, after which he gave the salam and performed two prostrations, then gave the salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3895