Shortening the Prayers (At-Taqseer)

Bukhari :: Book 2 :: Volume 20 :: Hadith 205

Narrated Hafs bin 'Asim:

Ibn 'Umar went on a journey and said, "I accompanied the Prophet and he did not offer optional prayers during the journey, and Allah says: 'Verily! In Allah's Apostle you have a good example to follow.' " (33.21)