Sahih Al Bukhari Hadith Number 1102

Narrated Ibn `Umar: I accompanied Allah’s Messenger (peace be upon him) and he never offered more than two rak`at during the journey. Abu Bakr, `Umar and `Uthman used to do the same.

18  Shortening the Prayers (At-Taqseer)
Hadith number 1102
Volume no 2
Chapter: 11 (Whoever did not offer the Nawafil before and after the (compulsory) Salat during a journey)