Muwatta Malik, Book 8, Hadith 20 (USC-MSA) ⓘ

Yahya related to me from Malik from Ismail ibn Muhammad ibn Said ibn Abi Waqqas from a mawla of Amr ibn al-As or of Abdullah ibn Amr ibn al-As that the Messenger of Allah, may Allah bless him and grant him peace, said, "The prayer of one of you sitting down is only equal to half the prayer of one of you when he is standing."

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ إِسْمَاعِيلَ بْنِ مُحَمَّدِ بْنِ سَعْدِ بْنِ أَبِي وَقَّاصٍ، عَنْ مَوْلًى، لِعَمْرِو بْنِ الْعَاصِ - أَوْ لِعَبْدِ اللَّهِ بْنِ عَمْرِو بْنِ الْعَاصِ - عَنْ عَبْدِ اللَّهِ بْنِ عَمْرِو بْنِ الْعَاصِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ صَلاَةُ أَحَدِكُمْ وَهُوَ قَاعِدٌ مِثْلُ نِصْفِ صَلاَتِهِ وَهُوَ قَائِمٌ ‏" ‏ ‏.‏