Imran bin Husayn (may Allah be pleased with him) said: I asked the Prophet (peace and blessings be upon him) about one who prays sitting, and he (peace and blessings be upon him) said: "Whoever prays standing, that is better; whoever prays sitting has half the reward of the one standing; and whoever prays lying down, his reward is half that of the one praying sitting."
(b) In the hadith of Ishaq: he asked the Prophet (peace and blessings be upon him) about one who prays sitting.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4592
Abdullah bin Amr (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "The reward of one who prays sitting is half that of one who prays standing."
(b) Jarir narrates from Mansur that praying sitting was a special characteristic of the Prophet (peace and blessings be upon him); and the meaning of his (peace and blessings be upon him) statement: "Praying sitting brings half the reward of one praying standing," will come in the chapter of special characteristics at the beginning of the Book of Marriage (Kitab al-Nikah), if Allah wills.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4593