(11) CHAPTER. Whoever did not offer the Nawafil (optional - non-obligatory) before and after the (compulsory) Salat (prayer) during a journey.
Narrated Ibn `Umar: I accompanied Allah's Apostle and he never offered more than two rak`at during the journey. Abu Bakr, `Umar and `Uthman used to do the same.
Authentic