From Sahih Bukhari (Hadith 1115):
Narrated `Imran bin Husain:(who had piles) I asked Allah's Messenger (ﷺ) 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
Reference: Bukhari 1115