Shortening the Prayers (At-Taqseer)

Bukhari :: Book 2 :: Volume 20 :: Hadith 206

Narrated Ibn 'Umar :

I accompanied Allah's Apostle and he never offered more than two Rakat during the journey. Abu Bakr, 'Umar and 'Uthman used to do the same.

Source materials are from the University of Southern California MSA site
Hadith eBooks converted from Imaan Star