Sahih Bukhari Volume 2, Book 20, Hadith Number 217.

Narated By ‘Abdullah bin Buraida : ‘Imran bin Husain had piles. Once Abu Ma mar narrated from ‘Imran bin Husain had said, “I asked the Prophet (p.b.u.h) about the prayer of a person while sitting. He said, ‘It is better for one to pray standing; and whoever prays sitting gets half the reward of that who prays while standing; and whoever prays while Lying gets half the reward of that who prays while sitting.’ “