It is narrated from Sayyiduna Imran bin Husayn (may Allah be pleased with him) that he - and he was a man of ease - asked the Messenger of Allah (peace and blessings be upon him) about praying sitting, and the Messenger of Allah (peace and blessings be upon him) said: "The prayer of one who sits is equal to half the prayer of one who stands, and the prayer of one who lies down is equal to half the prayer of one who sits."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15682