Shortening the Prayers (At-Taqseer)

Bukhari :: Book 2 :: Volume 20 :: Hadith 216

Narrated 'Imran bin Husain:

(who had piles) I asked Allah's Apostle about the praying of a man while sitting. He said, "If he prays while standing it is better and he who prays while sitting gets half the reward of that who prays standing; and whoever prays while Lying gets half the reward of that who prays while sitting."