Sahih Bukhari Volume 002, Book 020, Hadith Number 205.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 20. Shortening The Prayers (At-Taqseer)
Narated By 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)