Musannaf Ibn Abi Shayba 3:2255

Abu Bakr narrated to us, he said: Abu Usamah narrated to us, from Husayn al-Mu'allim, from Ibn Buraydah, from Imran ibn Husayn, that he asked the Prophet (peace be upon him) about praying while sitting. He said: "Pray standing, for it is better." Then he said: "The prayer of the one sitting is half of the prayer of the one standing, and the prayer of the one lying down is half of the prayer of the one sitting."