I asked the Messenger of Allah ﷺ about a man praying while seated. He said, "Whoever prays standing, that is best. Whoever prays sitting receives half the reward of one who prays standing, and whoever prays lying down receives half the reward of one who prays sitting."
حدثنا علي بن حجر حدثنا عيسى بن يونس حدثنا حسين المعلم عن عبد الله بن بريدة
سألت رسول الله ﷺ عن صلاة الرجل وهو قاعد فقال من صلى قائما فهو أفضل ومن صلى قاعدا فله نصف أجر القائم ومن صلى نائما فله نصف أجر القاعد
Bukhari narrated it in the chapter on Shortening [the Prayer], chapter: The prayer of one sitting, hadith: 1115, from the hadith of Husayn Muallim, with this wording.There are also narrations on this topic from Abdullah bin Amr [Muslim, hadith: 735], Anas [Abu Yaala, Tuhfat Ahwadhi: 1/293], Saaib [Ahmad: 425/3], and Ibn Umar [Bazzar, Kashf Astar: 274/1, hadith: 567, and Haythami graded it hasan in Majma: 149/2].