Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) said: I was told that the Prophet (peace and blessings be upon him) said: "A man's prayer while sitting carries half the reward of the prayer." I came to the Prophet of Allah (peace and blessings be upon him) and found him praying sitting, so I put my hand on my head. He (peace and blessings be upon him) said: "What is the matter with you, O Abdullah bin Amr?" I said: O Messenger of Allah (peace and blessings be upon him), I was told that you said this, and you yourself are praying sitting? He (peace and blessings be upon him) said: "Yes, but I am not like any one of you."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13388