(17) CHAPTER. To offer Salat (prayers) while sitting.
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.
Authentic