Sahih al-Bukhari 1115
صحيح البخاري#1115SahihNarrated `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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 18:35