(5) CHAPTER. When a traveller leaves his original place, he can shorten his Salat (prayers).
Narrated Anas bin Malik: offered four rak`at of Zuhr prayer with the Prophet (p.b.u.h) at Medina and two rak`at at Dhul-Hulaifa. (i.e. shortened the `Asr prayer).
Narrated `Aisha: When the prayers were first enjoined they were of two rak`at each. Later the prayer in a journey was kept as it was but the prayers for non-travelers were completed. Az-Zuhri said, I asked `Urwa what made Aisha pray the full prayers (in journey). He replied, She did the same as `Uthman did.