Shortening the Prayers (At-Taqseer)

Bukhari :: Book 2 :: Volume 20 :: Hadith 212

Narrated Anas bin Malik:

Whenever the Prophet started a journey before noon, he used to delay the Zuhr prayer till the time of 'Asr and then offer them together; and if the sun declined (at noon) he used to offer the Zuhr prayer and then ride (for the journey).