Sunan Ibn Majah, Volume 2, Book 5, Hadith 1230 (DarusSalam) ⓘ
It was narrated from Anas bin Malik that the Messenger of Allah went out and saw some people praying while sitting down. He said: “The prayer of one who sits down is equivalent to half of the prayer of one who stands.”
حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا بِشْرُ بْنُ عُمَرَ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ جَعْفَرٍ، حَدَّثَنِي إِسْمَاعِيلُ بْنُ مُحَمَّدِ بْنِ سَعْدٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ خَرَجَ فَرَأَى أُنَاسًا يُصَلُّونَ قُعُودًا فَقَالَ " صَلاَةُ الْقَاعِدِ عَلَى النِّصْفِ مِنْ صَلاَةِ الْقَائِمِ " .
also referenced under: Hadith 1230 (Reference) & Book 5, Hadith 1288 (In-Book)