Sahih Bukhari

Narrated By Abu Huraira : Allah's Apostle finished his prayer after offerings two Rakat only. Dhul-Yaddain asked him whether the prayer had been reduced, or you had forgotten?" The Prophet said, "Is Dhul-Yaddain speaking the truth?" The people said, "Yes." Then Allah's Apostle stood up and performed another two Rakat and then finished prayer with Taslim, and then said the Takbir and performed a prostration similar to or longer than his ordinary prostrations; then he raised his head, said Takbir and prostrated and then raised his head (Sahu prostrations).