Prayers (Salat)

Bukhari :: Book 1 :: Volume 8 :: Hadith 346

Narrated 'Aisha:

the mother of believers: Allah enjoined the prayer when He enjoined it, it was two Rakat only (in every prayer) both when in residence or on journey. Then the prayers offered on journey remained the same, but (the Rakat of) the prayers for non-travellers were increased.