Musnad Ahmad 790:145

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Khalid, from Abu Qilabah, from Abu al-Muhallab, from ‘Imran ibn Husayn, who said: The Messenger of Allah (peace and blessings of Allah be upon him) prayed Dhuhr or ‘Asr [and prayed] three rak‘ahs, then he performed the taslim. A man from the companions of the Prophet (peace and blessings of Allah be upon him), who was called al-Khirbaq, said: "Has the prayer been shortened?" The Prophet (peace and blessings of Allah be upon him) asked [the others], and it was as he said. He said: "So he prayed a rak‘ah, then he performed the taslim, then he prostrated two prostrations, then he performed the taslim."