Mishkat al-Masabih 1252
‘Abdallah b. ‘Amr said:
I was told that God’s Messenger had said, “Prayer engaged in by a man while sitting counts as half the prayer,” so I went to him and I found him praying while sitting, and I put my hand on his head. He said, “What is the matter with you, ‘Abdallah b. ‘Amr? ’’ I replied, “I have been told, Messenger of God, that you said that prayer engaged in by a man while sitting counts as half the prayer, yet you yourself are praying while sitting.” He said, “Yes, but I am not like one of you.” 

Muslim transmitted it.
عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو قَالَ: حُدِّثْتُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «صَلَاةُ الرَّجُلِ قَاعِدًا نِصْفُ الصَّلَاةِ» قَالَ: فَأَتَيْتُهُ فَوَجَدْتُهُ يُصَلِّي جَالِسًا فَوَضَعْتُ يَدِي عَلَى رَأسه فَقَالَ: «مَالك يَا عَبْدَ اللَّهِ بْنَ عَمْرٍو؟» قُلْتُ: حُدِّثْتُ يَا رَسُولَ اللَّهِ أَنَّكَ قُلْتَ: «صَلَاةُ الرَّجُلِ قَاعِدًا عَلَى نِصْفِ الصَّلَاةِ» وَأَنْتَ تُصَلِّي قَاعِدًا قَالَ: «أَجَلْ وَلَكِنِّي لَسْتُ كَأَحَدٍ مِنْكُمْ» . رَوَاهُ مُسلم