It was narrated from Anas bin Malik that the Messenger of Allah ﷺ 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 ﷺ خَرَجَ فَرَأَى أُنَاسًا يُصَلُّونَ قُعُودًا فَقَالَ " صَلاَةُ الْقَاعِدِ عَلَى النِّصْفِ مِنْ صَلاَةِ الْقَائِمِ " .