Sahih Bukhari Volume 002, Book 022, Hadith Number 318.
Narated By Abu Huraira : The Prophet led us in the 'Asr or the Zuhr prayer and finished it with Taslim. Dhul-Yadain said to him, "O Allah's Apostle! Has the prayer been reduced?" The Prophet asked his companions in the affirmative. So Allah's Apostle I offered two more Rakat and then performed two prostrations (of Sahu). Sad said, "I saw that 'Ursa bin Az-Zubair had offered two Rakat in the Maghrib prayer and finished it with Taslim. He then talked (and when he was informed about it) he completed the rest of his prayer and performed two prostrations, and said, 'The Prophet prayed like this.'"