The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1188
Imran b. Husain reported: The Messenger of Allah (may peace be upon him) said three rak'ahs of the 'Asr prayer and then got up and went to his apartment. A man possessing large arms stood up and said: Messenger of Allah, bias the player been shortened? He came out angrily, and said the rak'ah which he had omitted and then gave salutation. then performed two prostrations of forgetfulness and then gave salutation.