Shortening the Prayers (At-Taqseer)

Bukhari :: Book 2 :: Volume 20 :: Hadith 188

Narrated 'Abdullah bin 'Umar:

I offered the prayer with the Prophet, Abu Bakr and 'Umar at Mina and it was of two Rakat. 'Uthman in the early days of his caliphate did the same, but later on he started praying the full prayer.