Sunan an-Nasa'i 1660
سنن النسائي#1660SahihIt was narrated that 'Imran bin Husain said:"I asked the Prophet (ﷺ) about one who prays sitting down. He said: 'Whoever prays standing up is better, and one who prays sitting down will have half the reward of one who prays standing up. And whoever prays lying down will have half the reward of one who prays sitting down
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih Bukhari
In-book reference: 20:63